Wound treatment apparatus and method

ABSTRACT

An apparatus and method for aspirating, irrigating and/or cleansing wounds is provided. The apparatus and method include one or more of the following: simultaneous aspiration and irrigation of the wound, supplying of thermal energy to fluid circulated through the wound; supplying physiologically active agents to the wound; a biodegradable scaffold in contact with the wound bed; and application of stress or flow stress to the wound bed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/012,164, filed Aug. 28, 2013, which is a continuation of U.S.application Ser. No. 12/976,949, filed Dec. 22, 2010, which is acontinuation-in-part of U.S. application Ser. No. 10/599,722, filed Sep.19, 2008, which is a National Phase of PCT International Application No.PCT/GB2005/001603, filed Apr. 27, 2005, designating the United Statesand published on Mar. 11, 2005 as WO/2005/102415, which claims priorityto Great Britain Patent Application No. 0409446.2, filed Apr. 28, 2004.U.S. application Ser. No. 12/976,949 is also a continuation-in-part ofU.S. application Ser. No. 10/599,725, filed Sep. 22, 2008, which is aNational Phase of PCT International Application No. PCT/GB2005/001595,filed Apr. 27, 2005, designating the United States and published on Oct.11, 2005 as WO/2005/105179, which claims priority to Great BritainApplication No. 0409444.7, filed Apr. 27, 2004. U.S. application Ser.No. 12/976,949 is also a continuation-in-part of U.S. application Ser.No. 10/599,728 filed Nov. 3, 2008, which is a U.S. National Phase of thePCT International Application No. PCT/GB2005/001612, filed on Apr. 27,2005, designating the United States and published on Oct. 11, 2005 asWO/2005/105180, which claims priority to Great Britain PatentApplication No. 0409443.9, filed Apr. 28, 2004. U.S. application Ser.No. 12/976,949 is also a continuation-in-part of U.S. application Ser.No. 11/577,642, filed Aug. 23, 2007, which is a National Phase of PCTInternational Application No. PCT/GB05/04177, filed Oct. 28, 2005,designating the United States and published on May 4, 2006 asWO/2006/046060, which claims priority to Great Britain PatentApplication No. 0424046.1, filed Oct. 29, 2004. U.S. application Ser.No. 12/976,949 is also a continuation-in-part of U.S. application Ser.No. 11/919,355, filed Nov. 17, 2008, which is a National Phase of PCTInternational Application No. PCT/GB2006/001551, filed Apr. 27, 2006,designating the United States and published on Nov. 2, 2006 asWO/2006/114637, which claims priority to Great Britain PatentApplication No. 0508528.7, filed Apr. 27, 2005. U.S. application Ser.No. 12/976,949 is also a continuation-in-part of U.S. application Ser.No. 11/919,369, filed Nov. 17, 2008, which is a National Phase of PCTInternational Application No. PCT/GB2006/001625, filed on Apr. 27, 2006,designating the United States and published on Nov. 2, 2006 asWO/2006/114648, which claims priority to Great Britain PatentApplication No. 0508529.5, filed on Apr. 27, 2005. U.S. application Ser.No. 12/976,949 is also a continuation-in-part of U.S. application Ser.No. 12/066,578, filed Oct. 10, 2008, which is a U.S. National Phase ofthe PCT International Application No. PCT/GB06/03421, filed on Sep. 15,2006, designating the United States and published on Mar. 22, 2007 asWO/2007/031762, which claims priority to Great Britain PatentApplication No. 0518825.5, filed Sep. 15, 2005. The disclosures of theseprior applications are hereby incorporated by reference in theirentireties and should be considered part of this specification.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an apparatus and a medical wounddressing for aspirating, irrigating, and/or cleansing wounds, and amethod of treating wounds using such apparatus for aspirating,irrigating, and/or cleansing wounds.

It relates in particular to such an apparatus, wound dressing and methodthat can be easily applied to a wide variety of, but in particularchronic, wounds, to cleanse them of materials that are deleterious towound healing, whilst distributing materials that are beneficial in sometherapeutic aspect, in particular to wound healing.

Description of the Related Art

Aspirating and/or irrigating apparatus are known, and tend to be used toremove wound exudate during wound therapy. In known forms of such woundtherapy, aspiration and irrigation of the wound generally take placesequentially.

Such known forms of aspiration and/or irrigation therapy systems alsooften create a wound environment that may result in the loss of optimumperformance of the body's own tissue healing processes, and slowhealing, and/or in weak new tissue growth that does not have a strongthree-dimensional structure adhering well to and growing from the woundbed. This is a significant disadvantage, in particular in chronicwounds.

SUMMARY OF THE INVENTION

Certain embodiments of the present invention are directed to anaspirating and/or irrigating apparatus that may be used to remove woundexudate during wound therapy. Each part of the therapy cycle isbeneficial in promoting wound healing:

Aspiration applies a negative pressure to the wound, which is beneficialin itself in promoting wound healing by removing materials deleteriousto wound healing with the wound exudate, reducing bacterial load,combating peri-wound oedema, increasing local blood flow to the woundand encouraging the formation of wound bed granulation tissue.

Irrigation cleanses wounds of materials that are deleterious to woundhealing by diluting and moving wound exudate (which is typicallyrelatively little fluid and may be of relatively high viscosity andparticulate-filled).

Relatively little of beneficial materials involved in promoting woundhealing (such as cytokines, enzymes, growth factors, extracellular cellmatrix components and fragments thereof, biological signalling moleculesand other physiologically active components of the exudate) are presentin a wound, and are not well distributed in the wound, i.e. they are notnecessarily present in parts of the wound bed where they can bepotentially of most benefit. These may be distributed by irrigation ofthe wound and thus aid in promoting wound healing. The irrigant maycontain active materials that are potentially or actually beneficial inrespect of wound healing, such as nutrients for wound cells to aidproliferation, and gases, such as oxygen. These may be distributed byirrigation of the wound and thus aid in promoting wound healing.

If aspiration and irrigation therapy is applied sequentially to a wound,the two therapies, each of which is beneficial in promoting woundhealing, can only be applied intermittently. Thus, the wound will losethe abovementioned known beneficial effects of aspiration therapy onwound healing, at least in part, while that aspiration is suspendedduring irrigation.

Additionally, for a given aspirate flow, whilst materials that arepotentially or actually deleterious in respect of wound healing areremoved from wound exudate, the removal in a given time period ofapplication of the total irrigate and/or aspirate therapy will normallybe less effective and/or slower than with continuous application ofaspiration.

Even less to be desired, is that while aspiration is not applied to thewound, wound exudate and materials deleterious to wound healing (such asbacteria and debris, and iron II and iron III and for chronic woundsproteases, such as serine proteases) will pool on the wound bed andhinder wound healing, especially in a highly exuding wound. The influxof local oedema will also add to the chronicity of the wound. This isespecially the case in chronic wounds.

Depending on the relative volumes of irrigant and wound exudate, themixed exudate-irrigant fluid and may be of relatively high viscosityand/or particulate-filled. Once it is present and has pooled, it may bemore difficult to shift by the application of aspiration in aconventional sequential aspirate—irrigate—dwell cycle than withcontinuous simultaneous aspiration and irrigation of the wound, owing tothe viscosity and blockage in the system.

The wound will also lose the abovementioned beneficial effects ofirrigation therapy on wound healing, at least in part, while thatirrigation is suspended during aspiration. These benefits in promotingwound healing include the movement of materials that are beneficial inpromoting wound healing, such as those mentioned above, and the supplyin the irrigant of active amounts of materials that are beneficial inpromoting wound healing which pass into and/or through the wound incontact with the wound bed.

Additionally, for a given irrigant flow, the cleansing of the wound andthe distribution by irrigation of the wound of such beneficial materialsand the supply in the irrigant of active amounts of materials that arebeneficial in promoting wound healing in a given time period ofapplication of the total irrigate and/or aspirate therapy when suchtherapy is in a conventional sequential aspirate—irrigate—dwell cyclewill normally be less effective and/or slower than with continuousapplication of aspiration.

Additionally, aspirating and/or irrigating apparatus may be used for thedelivery from cells or tissue of further materials that are beneficialin promoting wound healing. Examples of the latter include materialsfrom cells or tissue, such as growth factors, extracellular matrixcomponents and fragments thereof, selective proteases or fibrinolyticfactors and combinations thereof.

It thus would be desirable to provide a system of aspiration andirrigation therapy for a wound, which can remove wound exudate andmaterials deleterious to wound healing from contact with the wound bed,whilst simultaneously cleansing it and distributing materials that arebeneficial in promoting wound healing from cells or tissue across it. Insome embodiments it would also be desirable to supply in the irrigantactive amounts of materials that are beneficial in promoting woundhealing which pass into and/or through the wound in contact with thewound bed. In some embodiments, it would be desirable to make the systemportable.

Another advantage, in particular in chronic wounds, in providingapparatus for aspirating, irrigating, and/or cleansing a wound accordingto certain embodiments of the present invention is that it providesmeans for providing more than one therapy continuously in a singledressing. Embodiments of the present invention provide several furtheradvantages.

One is that application of an irrigant to a wound under simultaneousaspiration and/or heating creates a wound environment that is exposed tothe continuous beneficial effects of both aspects of the therapy forwound healing as opposed to the sequential intermittent application ofirrigant flow and aspiration and/or heating in known aspirating and/orirrigating apparatus. The latter result in less than optimum performanceof the body's own tissue healing processes, and slower healing, and/orweaker tissue growth that does not have a strong three-dimensionalstructure adhering well to and growing from the wound bed. This is asignificant disadvantage, in particular in chronic wounds.

Thus, the use of the apparatus for aspirating, irrigating, and/orcleansing wounds retains and enhances the beneficial effects ofaspiration in respect of wound healing by continuous and preferablyconstant aspiration. These include removing materials deleterious towound healing with the wound exudate, reducing bacterial load, combatingperi-wound oedema and encouraging the formation of wound bed granulationtissue.

Preferred embodiments of the apparatus for aspirating, irrigating,and/or cleansing chronic wounds apply a milder negative pressure than inconventional negative pressure therapy (which is too aggressive for thefragile tissues of many such wounds). This leads to increased patientcomfort, and lessens the risk of inflammation of the wound. The removalof wound exudate in a given time period of application of thesimultaneous irrigate and/or aspirate therapy will normally be moreeffective and/or faster than with a conventional sequential intermittentaspiration and/or irrigation therapy.

Even more desirably, since simultaneous aspiration and irrigation isapplied to the wound, wound exudate and materials deleterious to woundhealing (such as bacteria and debris, and iron II and iron III and forchronic wounds proteases) will not pool on the wound bed and hinderwound healing especially in a highly exuding wound. This is especiallyimportant in highly exuding wounds, e.g. chronic wounds. The resultingmixed exudate-irrigant fluid will usually be of relatively lowerviscosity.

Because simultaneous aspiration and irrigation of the wound providescontinuous removal at a constant relatively high speed, the fluid doesnot have to be accelerated cyclically from rest, and will be easier toshift than with known forms of aspiration and/or irrigation therapysystems with a conventional sequential aspirate—irrigate—dwell cycle.This will thus exert a greater net effect on the removal of adherentbacteria and debris. This is especially the case in those embodiments ofthe apparatus for aspirating, irrigating, and/or cleansing wounds wherethere is an inlet manifold (as described in further detail hereinafter)that covers and contacts most of the wound bed (scaffold) with openingsthat deliver the fluid directly to the wound bed (scaffold) over anextended area.

Additionally, it is generally believed that the body's own metabolicactivities are at an optimum at or near the temperature naturallyoccurring in the relevant bodily part. Examples of metabolic moleculesinvolved in tissue healing processes that are beneficial in promotingwound healing include enzymes, growth factors and anti-inflammatories,and other physiologically active components of the exudate from a wound.These are believed to act best at temperatures found in the relevantbodily part in which they occur, varying between normal temperaturesfound at the body surface and those at the body core. The body core isat a higher temperature than the surface, but surface temperatures at33° C. and above are still relatively close to core body temperatures of36 to 38° C. (‘normothermic temperature’). Wounds, and in particularchronic wounds, may have a lower temperature, e.g. 24 to 26° C., i.e.substantially below the optimum temperature. Thus, the temperature ofthe wound itself is deleterious to wound healing.

This may result in slow wound healing, loss of cell proliferation,and/or growth that does not have a strong three-dimensional structureadhering well to and growing from the wound bed. Conventional woundaspiration and/or irrigation therapy systems thus often create a woundenvironment under a backing layer where (a) not only are beneficialmaterials lost to the site where they can be potentially of mostbenefit, i.e. the wound bed, when such therapy is applied, but (b) thewound healing processes, e.g. enzymic activity on tissue growth, areinhibited by sub-optimal temperatures. Heated dressings are known, butsuch forms of wound dressing do not simultaneously irrigate the woundenvironment under the backing layer. This will result in materialsdeleterious to wound healing in wound exudate being retained in thewound environment and hindering wound healing in spite of anystimulation of wound healing from wound temperature regulation.

There would thus be an advantage, in particular in chronic wounds, inproviding means for more than one therapy in a single dressing (a) whichnot only removes materials deleterious to wound healing from woundexudate, whilst distributing materials that are beneficial in promotingwound healing in contact with the wound bed, but (b) promotes woundhealing by creating a wound environment under the dressing withtemperatures which stimulate the activity of metabolic molecules thatare beneficial in promoting wound healing, e.g. temperatures near 36 to38° C. (‘normothermic temperature’).

A disadvantage of known heated wound dressings is that it is imperativebut not easy to avoid the heater, especially an electrical heater, fromscorching the wound and/or surrounding surfaces. This is especially sowhen the dressing is in contact with the wound bed. Several devices forapplying a dressing to the wound have been proposed. In one form, astiff flange or lip extends around the periphery of the dressing tospace the surface of the wound in use away from the heater. Such a wounddressing is cumbersome. Whilst it may be acceptable for hospital use,the stiff flange does little for patient comfort, and heightens the riskof inflammation of a wound and/or the leakage of wound exudate. Therewould be a further advantage in providing such a wound dressing thatconforms to the shape of the bodily part to which it is applied.

In the prior art devices, vascular supply to, and circulation oraspiration in, tissue underlying and surrounding the wound is oftencompromised. Therefore, certain embodiments of the present inventionprovide a system of therapy that also promotes vascular supply to tissueunderlying and surrounding a wound, promoting wound healing.

Certain embodiments of the present invention also provide a system oftherapy which creates flow stress or strain across the wound bedsurface, e.g. a shear flow gradient, e.g. by passing irrigant and/orwound exudate through the wound in a controllable stream, and optionallytissue surrounding the wound, e.g. by applying an optionally varyingpositive and/or negative pressure to the wound. Such a flow stressacross a cell containing surface such as the wound bed, e.g. a shearflow gradient, has been found to result in effects that may bebeneficial for wound healing.

According to one embodiment, an apparatus for aspirating, irrigating,and/or cleansing of wounds comprises (a) a fluid flow path, comprising aconformable wound dressing, having a backing layer which is capable offorming a relatively fluid-tight seal or closure over a wound and atleast one inlet pipe for connection to a fluid supply tube, which passesthrough and/or under the wound-facing face, and at least one outlet pipefor connection to a fluid offtake tube, which passes through and/orunder the wound-facing face to allow irrigation and/or aspiration of awound, and wherein the point at which the at least one inlet pipethrough and/or under the wound-facing face forming a relativelyfluid-tight seal or closure over the wound; (b) a fluid reservoirconnected by a fluid supply tube to an inlet pipe via optional means forsupply flow regulation; (c) optionally means for aspirate flowregulation, connected to a fluid offtake tube; (d) optionally means forsupplying physiologically active agents to the wound; and (e) at leastone device for moving fluid through the wound dressing; characterised inthat it comprises (f) means for providing simultaneous aspiration andirrigation of the wound, such that fluid may be supplied to fill theflowpath from the fluid reservoir via the fluid supply tube (optionallyvia means for supply flow regulation) while fluid is aspirated by adevice through the fluid offtake tube (optionally or as necessary viameans for aspirate flow regulation).

In another embodiment, the apparatus further comprises means forsupplying thermal energy to the wound. In another embodiment, abiodegradable scaffold is located under the backing layer and configuredto be placed in contact with a wound bed in use. In another embodiment,means for applying flow stress to the wound bed is also provided.

Where any pipe is described in connection with the operation of theapparatus as being connected or for connection to a (mating end of a)tube, e.g. a fluid supply tube, fluid offtake tube, the pipe and thetube may form a single integer in the flow path through which thecirculating fluid from the wound passes.

Described below are examples of components and characteristics that maybe included in the apparatus.

Fluid Reservoir and Container(s)

In one embodiment, the apparatus for aspirating, irrigating, and/orcleansing wounds is provided with means for admitting fluids directly orindirectly to the wound under the wound dressing in the form of a fluidsupply tube to a fluid reservoir. The fluid reservoir may be of anyconventional type, e.g. a tube, bag (such as a bag typically used forblood or blood products, e.g. plasma, or for infusion feeds, e.g. ofnutrients), chamber, pouch or other structure, e.g. of polymer film,which can contain the irrigant fluid.

The reservoir may be made of a film, sheet or membrane, often with a(generally uniform) thickness similar to that of films or sheets used inconventional wound dressing backing layers, i.e. up to 100 micron,preferably up to 50 micron, more preferably up to 25 micron, and of 10micron minimum thickness, and is often a resiliently flexible, e.g.elastomeric, and preferably soft, hollow body. In certain embodiments ofthe apparatus the type and material of the tubes throughout theapparatus for aspirating, irrigating, and/or cleansing wounds and thefluid reservoir will be largely determined by their function.

To be suitable for use, in particular on chronic timescales, thematerial should be non-toxic and biocompatible, inert to any activecomponents, as appropriate of the irrigant from the fluid reservoirand/or wound exudate in the apparatus flow path, and, in any use of atwo-phase system aspiration and irrigation unit, of the dialysate thatmoves into the aspirating fluid in the apparatus. When in contact withirrigant fluid, it should not allow any significant amounts ofextractables to diffuse freely out of it in use of the apparatus.

It should be sterilizable by ultraviolet, gamma or electron beamirradiation and/or with fluid antiseptics, such as solutions ofchemicals, fluid- and microbe-impermeable once in use, and flexible.Examples of suitable materials for the fluid reservoir include syntheticpolymeric materials, such as polyolefins, such as polyethylene, e.g.high-density polyethylene and polypropylene. Suitable materials for thepresent purpose also include copolymers thereof, for example with vinylacetate and mixtures thereof. Suitable materials for the present purposefurther include medical grade poly(vinyl chloride).

Notwithstanding such polymeric materials, the fluid reservoir will oftenhave a stiff area to resist any substantial play between it andcomponents that are not mutually integral, such as the fluid supply tubetowards the wound dressing, and may be stiffened, reinforced orotherwise strengthened, e.g. by a projecting boss.

The containers that contain the cell or tissue components may be, e.g.connected to a single supply tube by a Y-junction, and thence to thewound dressing, or they may, e.g. be connected to it by separate supplytubes, the two flows of physiologically active agents from cells ortissue optionally with irrigant and/or nutrient medium for the cellsbeing optionally mutually admixed in the wound space under the wounddressing. In an alternative layout of this means for supplyingphysiologically active agents from cells or tissue to the wound, thefirst container, in which the first input cell or tissue type iscontained, is in fluid communication in series with the secondcontainer, in which the second cell or tissue type is contained. Thus,they feed their physiologically active agents in series to the dressingand to the wound bed under the action of at least one device for movingfluid through the wound. In this layout of the means for supplyingphysiologically active agents from cells or tissue, the two containerseffectively function as a single container.

Irrigant and/or nutrient medium for the cells or tissue is often fedthrough the containers of the cell or tissue components and thence tothe wound dressing. In use, these layouts of the means for supplyingphysiologically active agents from cells or tissue to the wound willfunction in the apparatus exactly as for their analogues with a singlecell or tissue type. The container that contains a cell or tissuecomponent is often in the form of a hollow body such as an e.g. acanister, cartridge or cassette. It often has a chamber or compartmentthat contains a cell or tissue component, through which irrigant and/ora nutrient medium for the cells or tissue is passed. Where the containerthat contains a cell or tissue component lies outside the backing layer,the structure will often be made of glass, and/or synthetic polymericmaterials. For example, such a structure may be a glass cylinderdefining a chamber with axial inlet and outlet ports for throughflow,which contains cells or tissue on a scaffold.

Where the container that contains a cell or tissue component lies underthe backing layer, the structure will often be made of a conformablesynthetic polymeric material. Such a structure may still be a structuredefining a chamber with an inlet port, which contains cells or tissue ona scaffold, and which communicates with the wound via at least onechannel or conduit. The latter is/are for supplying physiologicallyactive agents from cells or tissue and irrigant to the wound under theaction of at least one device for moving fluid through the wound.

Where the container that contains a cell or tissue component is integralwith the other components of the dressing, in particular the backinglayer, it will usually be of the same polymeric material as thecomponents. Where, alternatively, it is permanently or demountablyattached to them/it, with an adhesive film, for example, or byheat-sealing, it may be of a different polymeric material. Any suchstructure may contain a cell or tissue component that is not bound to aninsoluble and immobilised substrate over and/or through which theirrigant and/or wound exudate from the wound dressing passes. It thenalso appropriately comprises two or more integers which are permeable tothe wound exudate or a mixture with irrigant, but have apertures, holes,openings, orifices, slits or pores of sufficiently small cross-dimensionto hold the cell or tissue component, and to retain particulates, e.g.cell debris, in the hollow body. Each of the integers may theneffectively form a macroscopic and/or microscopic filter.

Alternatively, it may contain a cell or tissue component that is boundto an insoluble and immobilised substrate over and/or through which theirrigant and/or wound exudate from the wound dressing passes, e.g. ascaffold. This will often be of a material that is not (cyto)toxic andis biocompatible and inert to any components that are beneficial inpromoting wound healing, including natural and synthetic polymericmaterials, which may typically in the form of a conformable film, sheetor membrane, often with apertures, holes, openings, orifices, slits orslots of small cross-dimension.

It may then effectively form a structure which is a mesh, grid, lattice,net or web. The container for cells or tissue may then not need tocomprise two or more integers which are permeable to the wound exudateor a mixture with irrigant to hold the cell or tissue component in thehollow body, but they may be desirable to retain particulates, e.g. celldebris. The container that contains the tissue or cell component willnormally be mounted within or in association with a device constructedto maintain the viability and activity of the cells. This would includebut not be limited to the means for supplying nutrition and regulatingthe exchange of gases and maintaining an optimum temperature.

The means for supplying nutrition may comprise a conventional nutrientmedium for the cells or tissue containing one or more physiologicallyactive component materials that are beneficial in promoting cellproliferation in the cells or tissue in the container that contains thecells or tissue and/or the expression by such cells or tissue of one ormore physiologically active component materials that are beneficial inpromoting wound healing.

Simultaneous Aspiration and Irrigation

The means for providing simultaneous aspiration and irrigation of thewound often comprises (a) a (first) device for moving fluid through thewound applied to fluid downstream of and away from the wound dressing,in combination with at least one of (b) a second device for moving fluidthrough the wound applied to the irrigant in the fluid supply tubeupstream of and towards the wound dressing; (c) means for aspirate flowregulation, connected to a fluid offtake tube, and (d) means for supplyflow regulation, connected to a fluid supply tube.

The (first) device is applied to the fluid in the fluid tube and/or thefluid in the fluid offtake tube downstream of and away from the wounddressing, and will usually apply negative pressure (i.e.below-atmospheric pressure or vacuum) to the wound bed. The (first)device will apply negative pressure (i.e. below-atmospheric pressure orvacuum) to the wound bed. It may be applied to the aspirate in the fluidofftake tube downstream of and away from the wound dressing. It may havemeans for aspirate flow regulation, such as a regulator, such as arotary valve connected between two parts of a fluid offtake tube, suchthat the desired supply flow regulation is achieved.

Alternatively or additionally, where appropriate, the aspirate in thefluid offtake tube downstream of the wound dressing may be aspiratedinto a collection vessel, and the first device may act on fluid such asair from the collection vessel. This prevents contact of the device withthe aspirate.

The (first) device may be a fixed-throughput device, such as afixed-speed pump, which will usually require a discrete means foraspirate flow regulation, connected to a fluid offtake tube, and/ormeans for supply flow regulation, connected to a fluid supply tube, ineach case, e.g. a regulator, such as a rotary valve.

Alternatively, where appropriate the (first) device for moving fluidthrough the wound may be a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integer.

The (first) device for moving fluid through the wound will often be apump of any of the following types, or a piped supply of vacuum, appliedto fluid downstream of and away from the wound dressing. In the case ofany pump it may be a fixed-speed pump, with (as above) a discrete meansfor aspirate flow regulation, connected to a fluid offtake tube, and/ormeans for supply flow regulation, connected to a fluid supply tube, ineach case, e.g. a regulator, such as a rotary valve. Alternatively,where appropriate the pump may be a variable-throughput orvariable-speed pump.

The following types of pump may be used as the (first) device: (a)reciprocating pumps, such as (i) Piston pumps—where pistons pump fluidsthrough check valves, in particular for positive and/or negativepressure on the wound bed; and (ii) Diaphragm pumps—where pulsations ofone or two flexible diaphragms displace liquid with check valves; and(b) Rotary pumps, such as: (i) Progressing cavity pumps with acooperating screw rotor and stator, in particular for higher-viscosityand particulate-filled exudate; and (ii) Vacuum pumps—with pressureregulators.

The (first) device may be a diaphragm pump, e.g. preferably a smallportable diaphragm pump. This is a preferred type of pump, in order inparticular to reduce or eliminate contact of internal surfaces andmoving parts of the pump with (chronic) wound exudate, and for ease ofcleaning.

Where the pump is a diaphragm pump, and preferably a small portablediaphragm pump, the one or two flexible diaphragms that displace liquidmay each be, for example a polymer film, sheet or membrane, that isconnected to means for creating the pulsations. This may be provided inany form that is convenient, inter alia as a piezoelectric transducer, acore of a solenoid or a ferromagnetic integer and coil in which thedirection of current flow alternates, a rotary cam and follower, and soon.

Where any second device is applied to the fluid in the fluid supply tubeupstream of and towards the wound dressing, it will usually applypositive pressure (i.e. above-atmospheric pressure) to the wound bed. Aswith the (first) device, it may be a fixed-throughput device, such as afixed-speed pump, which will usually require a discrete means for supplyflow regulation, connected to a fluid supply tube, e.g. a regulator,such as a rotary valve.

Alternatively, where appropriate the second device for moving irrigantfluid to the wound may be a variable-throughput device, such as avariable-speed pump, upstream of the wound dressing, thus effectivelyforming a combination of a second device for moving fluid through thewound with means for supply flow regulation in a single integer.

The second device for moving fluid through the wound will often be apump of any of the following types applied to the irrigant in the fluidsupply tube upstream of and towards the wound dressing. It may be afixed-speed pump, with (as above) a discrete means for supply flowregulation, connected to a fluid supply tube, e.g. a regulator, such asa rotary valve. Alternatively, where appropriate the pump may be avariable-throughput or variable-speed pump. It may have means foraspirate flow regulation, such as a regulator, such as a rotary valveconnected between two parts of a fluid offtake tube, such that thedesired supply flow regulation is achieved.

The following types of pump may be used as the second device: (a)Reciprocating pumps, such as (i) Shuttle pumps—with an oscillatingshuttle mechanism to move fluids at rates from 2 to 50 ml per minute;and (b) Rotary pumps, such as: (i) Centrifugal pumps, (ii) Flexibleimpeller pumps—where elastomeric impeller traps fluid between impellerblades and a moulded housing that sweeps fluid through the pump housing,(iii) Peristaltic pumps—with peripheral rollers on rotor arms acting ona flexible fluid aspiration tube to urge fluid current flow in the tubein the direction of the rotor, (iv) Rotary vane pumps—with rotatingvaned disk attached to a drive shaft moving fluid without pulsation asit spins. The outlet can be restricted without damaging the pump.

The second device may be a peristaltic pump, e.g. preferably a smallportable peristaltic pump. This is a preferred type of pump, in order inparticular to reduce or eliminate contact of internal surfaces andmoving parts of the pump with irrigant, and for ease of cleaning. Wherethe pump is a peristaltic pump, this may be e.g. an Instech Model P720miniature peristaltic pump, with a flow rate: of 0.2-180 ml/hr and aweight of <0.5 k. This is potentially useful for home and field hospitaluse.

Each such pump of any these types may also suitably be one that iscapable of pulsed, continuous, variable and/or automated and/orprogrammable fluid movement. Less usually and less preferably, each suchpump of any these types will be reversible.

As above, the means for supply flow regulation may be a regulator, suchas a rotary valve. This is connected between two parts of a fluid supplytube, such that the desired supply flow regulation is achieved. If thereare two or more inlet pipes, these may be connected to a single fluidsupply tube with a single regulator, or to first, second, etc. fluidsupply tubes, respectively having a first regulator, a second regulator,etc., e.g. a valve or other control device for admitting fluids into thewound.

As above, the means for aspirate flow regulation may be similarlyprovided in a form in which concomitant aspirate flow regulation ispossible. It may be a regulator, such as a valve or other controldevice, e.g. a rotary valve. Multiple offtake tubes may be similarlyprovided with single or multiple regulators for aspiration of fluidsfrom the apparatus, e.g. to an aspirate collection vessel, such as acollection bag. If there is no second device for moving fluid throughthe wound applied to the irrigant in the fluid supply tube upstream ofand towards the wound dressing, it is only possible to apply a negativepressure to the wound, by means of the device for moving fluid throughthe wound applied to the aspirate in the fluid offtake tube downstreamof and away from the wound dressing.

Operation may e.g. be carried out at a negative pressure of up to 50%atm., typically at a low negative pressure of up to 20% atm., moreusually up to 10% atm. at the wound, as is described hereinafter.

Examples of suitable and preferred (first) devices include those typesof pump that are so described hereinbefore in relation to the firstdevice. This may be a diaphragm pump, e.g. preferably a small portablediaphragm pump. This is a preferred type of pump, in order in particularto reduce or eliminate contact of internal surfaces and moving parts ofthe pump with (chronic) wound exudate, and for ease of cleaning.

Alternatively, if it is desired to apply a net positive pressure to thewound, the means for providing simultaneous aspiration and irrigation ofthe wound should comprise not only (a) a first device for moving fluidthrough the wound applied to the aspirate in the fluid offtake tubedownstream of and away from the wound dressing, but also (b) a seconddevice for moving fluid through the wound applied to the irrigant in thefluid supply tube upstream of and towards the wound dressing.

Operation may then e.g. be carried out at a positive pressure of up to50% atm., typically at a low positive pressure of up to 20% atm., moreusually up to 10% atm. at the wound, as is described hereinafter.

Examples of suitable and preferred first devices include those types ofpump that are so described hereinbefore in relation to the first device.This may be a diaphragm pump, e.g. preferably a small portable diaphragmpump. This is a preferred type of pump, in order in particular to reduceor eliminate contact of internal surfaces and moving parts of the pumpwith (chronic) wound exudate, and for ease of cleaning.

Examples of suitable and preferred second devices include those types ofpump that are so described hereinbefore in relation to the seconddevice. This may be a peristaltic pump, e.g. a miniature peristalticpump. This is a preferred type of pump, in order to eliminate contact ofinternal surfaces and moving parts of the pump with irrigant in thefluid supply tube upstream of and towards the wound dressing, and forease of cleaning.

It is of course equally possible to apply a negative pressure to thewound, by means of such a combination of (a) a first device for movingfluid through the wound applied to the aspirate in the fluid offtaketube downstream of and away from the wound dressing, and (b) a seconddevice for moving fluid through the wound applied to the irrigant in thefluid supply tube upstream of and towards the wound dressing; optionallywith (c) means for supply flow regulation, connected to a fluid supplytube; (d) means for aspirate flow regulation, connected to a fluidofftake tube.

Indeed, as noted below in this regard, preferred embodiments of theapparatus for aspirating, irrigating and/or cleansing chronic woundsthat apply a negative pressure include such types of combination of (a)a first device, e.g. a diaphragm pump, e.g. preferably a small portablediaphragm pump, and (b) a second device, e.g. a peristaltic pump,preferably a miniature peristaltic pump, as described hereinbefore inrelation to the device for moving fluid through the wound.

As noted above, either of the first device and the second device may be(a) a fixed-throughput device, such as a fixed-speed pump, which willusually require a discrete means for aspirate flow regulation, connectedto a fluid offtake tube, and/or means for supply flow regulation,connected to a fluid supply tube, in each case, e.g. a regulator, suchas a rotary valve, or (b) a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integer.

The higher end of the ranges of % positive and negative pressure and/orvacua noted above are potentially more suitable for hospital use, wherethey may only be used safely under professional supervision. The lowerend is potentially more suitable for home use, where relatively high %positive and negative pressures and/or vacua cannot be used safelywithout professional supervision, or for field hospital use. In eachcase, the pressure on the wound may be held constant throughout thedesired length of therapy, or may be varied cyclically in a desiredpositive or negative pressure regime.

As noted above, when it is desired to apply a negative pressure to thewound, it is preferred that the means for providing simultaneousaspiration and irrigation of the wound comprise not only (a) a (first)device for moving fluid through the wound applied to the aspirate in thefluid offtake tube downstream of and away from the wound dressing, butalso (b) a second device for moving fluid through the wound applied tothe irrigant in the fluid supply tube upstream of and towards the wounddressing.

Accordingly, one embodiment of the apparatus for irrigating, cleansingand/or aspirating wounds of the present invention is characterised inthe means for providing simultaneous aspiration and irrigation of thewound comprises (a) a (first) device for moving fluid through the woundapplied to fluid downstream of and away from the wound dressing, and (b)a second device for moving fluid through the wound applied to theirrigant in the fluid supply tube upstream of and towards the wounddressing, and in combination with at least one of (c) means for supplyflow regulation, connected to a fluid supply tube, and (d) means foraspirate flow regulation, connected to a fluid offtake tube.

As noted above, either of the first device and the second device may be(a) a fixed-throughput device, such as a fixed-speed pump, which willusually require a discrete means for aspirate flow regulation, connectedto a fluid offtake tube, and/or means for supply flow regulation,connected to a fluid supply tube, in each case, e.g. a regulator, suchas a rotary valve, or (b) a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integer.

This combination of (a) a device for moving fluid through the woundapplied to the aspirate in the fluid offtake tube downstream of and awayfrom the wound dressing, and (b) a device for moving fluid through thewound applied to the fluid in the fluid supply tube upstream of andtowards the wound dressing, may be used to apply an overall positive ornegative, or even zero pressure to the wound.

At least one body in the flow path to, over and from the wound bedshould have sufficient resilience against the pressure to allow anysignificant compression or decompression of the fluid occur. Thus,examples of suitable bodies include those which are or are defined by afilm, sheet or membrane, such as inlet or offtake and/or tubes andstructures such as bags, chambers and pouches, filled with irrigantfluid, and e.g. the backing layer of the wound dressing, made ofelastically resilient thermoplastic materials.

It will be seen that the balance of fluid between aspirated fluid fromthe wound and irrigant supplied to the wound from the fluid reservoirwill thus be largely determined by a means for providing simultaneousaspiration and irrigation of the wound which is a system comprising: (a)means for aspirate flow regulation and/or a device for moving fluidthrough the wound applied to fluid downstream of and away from the wounddressing, and (b) means for supply flow regulation and/or a device formoving fluid through the wound applied to the fluid in the fluid supplytube upstream of and towards the wound dressing.

As noted above, either of the first device and the second device may be(a) a fixed-throughput device, such as a fixed-speed pump, which willusually require a discrete means for aspirate flow regulation, connectedto a fluid offtake tube, and/or means for supply flow regulation,connected to a fluid supply tube, in each case, e.g. a regulator, suchas a rotary valve, or (b) a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integer.

At least one body in the flow path to, over and from the wound bedshould have sufficient resilience against the pressure to allow anysignificant compression or decompression of the fluid occur. Thus,examples of suitable bodies include those which are or are defined by afilm, sheet or membrane, such as inlet or offtake and/or tubes andstructures such as bags, chambers and pouches, filled with irrigantfluid, and e.g. the backing layer of the wound dressing, made ofelastically resilient thermoplastic materials.

It will be seen that the balance of fluid between aspirated fluid fromthe wound and irrigant supplied to the wound from the fluid reservoirwill thus be largely determined by a means for providing simultaneousaspiration and irrigation of the wound which may be a system comprising:(a) means for aspirate flow regulation and/or a device for moving fluidthrough the wound applied to fluid downstream of and away from the wounddressing, and (b) means for supply flow regulation and/or a device formoving fluid through the wound applied to the fluid in the fluid supplytube upstream of and towards the wound dressing.

The same means may be used to apply an overall positive or negative, oreven neutral pressure to the wound. The means may also be used to varythe pressure in the wound dressing (e.g. via a manifold) to apply stressto the wound bed and optionally areas surrounding the wound.

The appropriate flow rate through the supply tube will depend on anumber of factors, such as (a) The components of the irrigant and/orwound exudate, the relative volumes of irrigant and wound exudate, (b)the viscosity and consistency of each of the irrigant, exudate and mixedexudate-irrigant fluid, and any changes as the wound heals; (c) thelevel of negative pressure on the wound bed, (d) whether the irrigant inthe fluid supply tube upstream of and into the wound dressing is underpositive pressure, and the level of such pressure; (e) the level of anypressure drop between the irrigant in the fluid supply tube upstream ofthe wound dressing and the wound bed, such as across a porous element,e.g. a membrane scaffold on the lower surface of an inlet manifold thatdelivers the fluid directly to the wound bed; means for supply flowregulation; and/or a second device for moving fluid through the woundapplied to the fluid in the fluid supply tube upstream of and towardsthe wound dressing; (f) the depth and/or capacity of the wound and (g)the power consumption needed for a given desired fluid volume flow rateof irrigant and/or wound exudate through the wound.

It may also depend on the level of any pressure drop between theirrigant in the fluid supply tube upstream of the wound dressing and thewound bed, such as across a porous element, e.g. a membrane scaffold onthe lower surface of an inlet manifold that delivers the fluid directlyto the wound bed; means for supply flow regulation; and/or a seconddevice for moving fluid through the wound applied to the fluid in thefluid supply tube upstream of and towards the wound dressing;

The dressing may comprise an inlet manifold (as described in furtherdetail hereinafter) that covers and contacts a significant area,preferably most of the wound bed with openings that deliver the fluiddirectly to the wound bed over an extended area, in the form of one ormore inflatable hollow bodies defined by a film sheet or membrane. Ingeneral a manifold will cover 50% of the wound, preferably 75% or more,though it is possible that it may cover a smaller area of the wound. The(usually small) positive pressure above atmospheric from the irrigationdevice when both devices are running together should be sufficient toinflate the manifold.

The desired fluid volume flow rate of irrigant and/or wound exudate ispreferably that for optimum performance of the wound healing process.The flow rate will usually be in the range of 1 to 1500 ml/hr, such as 5to 1000 ml/hr, e.g. 15 to 300 ml/hr, such as 35 to 200 ml/hr through thesupply tube. The flow rate through the wound may be held constantthroughout the desired length of therapy, or may be varied cyclically ina desired flow rate regime.

In practice, the offtake rate of flow of total irrigant and/or woundexudate will generally be of the order of 1 to 2000, e.g. 35 to 300ml/24 hr/cm², where the cm² refers to the wound area, depending onwhether the wound is in a highly exuding state.

In practice, the rate of exudate flow is typically only of the order ofup to 75 microlitres/cm²/hr (where cm² refers to the wound area), andthe fluid can be highly mobile or not, depending on the level ofproteases present). Exudate levels drop and consistency changes as thewound heals, e.g. to a level for the same wound that equates to 12.5-25microlitres/cm²/hr.

It will be seen that the aspirated fluid from the wound will typicallycontain a preponderance of irrigant from the fluid reservoir over woundexudate. The necessary adjustments to maintain the desired balance offluid by means of (a) the means for aspirate flow regulation and/ordownstream device, and (b) the means for supply flow regulation and/orupstream device for moving fluid will be apparent to the skilled person,bearing in mind that as noted above, either of the first device and thesecond device may be (i) a fixed-throughput device, such as afixed-speed pump, which will usually require a discrete means foraspirate flow regulation, connected to a fluid offtake tube, and/ormeans for supply flow regulation, connected to a fluid supply tube, ineach case, e.g. a regulator, such as a rotary valve, or (ii) avariable-throughput device, such as a variable-speed pump, downstream ofthe wound dressing, thus effectively forming a combination of a (first)device for moving fluid through the wound with means for aspirate flowregulation and/or means for supply flow regulation in a single integer.

The type and/or capacity of a suitable first device for moving fluidthrough the wound applied to the aspirate in the fluid offtake tubedownstream of and away from the wound dressing and/or a suitable seconddevice for moving fluid through the wound applied to the irrigant in thefluid supply tube upstream of and towards the wound dressing and/or willbe largely determined by (a) the appropriate or desired fluid volumeflow rate of irrigant and/or wound exudate from the wound, and (b)whether it is appropriate or desired to apply a positive or negativepressure to the wound bed, and the level of such pressure to the woundbed for optimum performance of the wound healing process, and by factorssuch as portability, power consumption and isolation from contamination.

As noted above, when it is desired to apply a negative pressure to thewound with the apparatus for aspirating, irrigating and/or cleansingwounds to provide simultaneous aspiration and irrigation of the wound,the means for providing simultaneous aspiration and irrigation of thewound may comprise (a) a single device for moving fluid through thewound applied to the aspirate in the fluid offtake tube downstream ofand away from the wound dressing or in combination with at least one of(b) means for supply flow regulation, connected to a fluid supply tube,and (c) means for aspirate flow regulation, connected to a fluid offtaketube.

As noted above, the device may be (a) a fixed-throughput device, such asa fixed-speed pump, which will usually require a discrete means foraspirate flow regulation, connected to a fluid offtake tube, e.g. aregulator, such as a rotary valve, or (b) a variable-throughput device,such as a variable-speed pump, downstream of the wound dressing, thuseffectively forming a combination of a device for moving fluid throughthe wound with means for aspirate flow regulation in a single integer.

In a preferred embodiment the apparatus has at least one inlet pipe andat least one outlet pipe, each of which passes through and/or under thewound-facing face. Such an embodiment allows for a method simultaneousand/or sequential irrigation/aspiration of the wound. In such anembodiment step (d) of the method comprises activating the at least onedevice of moving fluid through the wound dressing to move fluid(irrigant) through the at least one inlet and to move fluid (aspirate)out of the at least one outlet pipe.

In a preferred embodiment the irrigant is moved to the wound via theinlet pipe and aspirate removed from the outlet pipe simultaneously,i.e. simultaneous irrigation/aspiration. This may be carried out forsubstantially the entirety of the treatment of the wound, or alternatelyfor portions of the treatment as desired.

Such an embodiment is also suitable for sequential (fill/empty)operation, and thus a method wherein sequential operation is carried outforms an alternative embodiment of the invention. In such an embodimentirrigation would be ceased by ceasing the device moving fluid throughthe at least one inlet and activating a device to move fluid from thewound through the outlet.

Suitable flow rates, parameters for operation of the means for applyingstress and for operation of the apparatus in general are set out above.Further details are given below.

Conformable Wound Dressing

In certain embodiments of the apparatus for aspirating, irrigating,and/or cleansing wounds, a particular advantage is the tendency of thewound dressing to conform to the shape of the bodily part to which it isapplied.

The wound dressing comprises (a) a backing layer with a wound-facingface which is capable of forming a relatively fluid-tight seal orclosure over a wound and (b) at least one inlet pipe for connection to afluid supply tube or tube, which passes through and/or under thewound-facing face, and (c) at least one outlet pipe for connection to afluid offtake tube, which passes through and/or under the wound-facingface, the point at which the or each inlet pipe and the or each outletpipe passes through and/or under the wound-facing face forming arelatively fluid-tight seal or closure.

The term ‘relatively fluid-tight seal or closure’ is used herein toindicate one which is fluid- and microbe-impermeable and permits apositive or negative pressure of up to 50% atm., more usually up to 20%atm., e.g. up to 10% atm. to be applied to the wound. The term ‘fluid’is used herein to include gels, e.g. thick exudate, liquids, e.g. water,and gases, such as air, nitrogen, etc.

The shape of the backing layer that is applied may be any that isappropriate to aspirating, irrigating, and/or cleansing the wound acrossthe area of the wound. Examples of such include a substantially flatfilm, sheet or membrane, or a bag, chamber, pouch or other structure ofthe backing layer, e.g. of polymer film, which can contain the fluid.

The backing layer may be a film, sheet or membrane, often with a(generally uniform) thickness of up to 100 micron, preferably up to 50micron, more preferably up to 25 micron, and of 10 micron minimumthickness.

Its largest cross-dimension may be up to 500 mm (for example for largetorso wounds), up to 100 mm (for example for axillary and inguinalwounds), and up to 200 mm for limb wounds (for example for chronicwounds, such as venous leg ulcers and diabetic foot ulcers.

Desirably the dressing is resiliently deformable, since this may resultin increased patient comfort, and lessen the risk of inflammation of awound. Suitable materials for it include synthetic polymeric materialsthat do not absorb aqueous fluids, such as polyolefins, such aspolyethylene e.g. high-density polyethylene, polypropylene, copolymersthereof, for example with vinyl acetate and polyvinyl alcohol, andmixtures thereof; polysiloxanes; polyesters, such as polycarbonates;polyamides, e.g. 6-6 and 6-10, and hydrophobic polyurethanes. They maybe hydrophilic, and thus also include hydrophilic polyurethanes. Theyalso include thermoplastic elastomers and elastomer blends, for examplecopolymers, such as ethyl vinyl acetate, optionally or as necessaryblended with high-impact polystyrene. They further include elastomericpolyurethane, particularly polyurethane formed by solution casting.Preferred materials for the present wound dressing include thermoplasticelastomers and curable systems.

The backing layer is capable of forming a relatively fluid-tight seal orclosure over the wound and/or around the inlet and outlet pipe(s). Thebacking layer may be impermeable, semi-impermeable or otherwise.

However, in particular around the periphery of the wound dressing,outside the relatively fluid-tight seal, it is preferably of a materialthat has a high moisture vapour permeability, to prevent maceration ofthe skin around the wound. It may also be a switchable material that hasa higher moisture vapour permeability when in contact with liquids, e.g.water, blood or wound exudate. This may, e.g. be a material that is usedin Smith & Nephew's Allevyn™, IV3000™ and OpSite™ dressings.

The periphery of the wound-facing face of the backing layer may bear anadhesive film, for example, to attach it to the skin around the wound.This may, e.g. be a pressure-sensitive adhesive, if that is sufficientto hold the wound dressing in place in a fluid-tight seal around theperiphery of the wound-facing face of the wound dressing.

Alternatively or additionally, where appropriate a light switchableadhesive could be used to secure the dressing in place to preventleakage. (A light switchable adhesive is one the adhesion of which isreduced by photocuring. Its use can be beneficial in reducing the traumaof removal of the dressing.) Thus, the backing layer may have a flangeor lip extending around the proximal face of the backing layer, of atransparent or translucent material (for which it will be understoodthat materials that are listed above are amongst those that aresuitable). This bears a film of a light switchable adhesive to securethe dressing in place to prevent leakage on its proximal face, and alayer of opaque material on its distal face.

To remove the dressing and not cause excessive trauma in removal of thedressing, the layer of opaque material on the distal face of the flangeor lip extending around the proximal wound is removed prior toapplication of radiation of an appropriate wavelength to the flange orlip.

If the periphery of the wound dressing, outside the relativelyfluid-tight seal, that bears an adhesive film to attach it to the skinaround the wound, may be of a material that has a high moisture vapourpermeability or is a switchable material, then the adhesive film, ifcontinuous, should also have a high or switchable moisture vapourpermeability, e.g. be an adhesive such as used in Smith & Nephew'sAllevyn™, IV3000™ and OpSite™ dressings.

Where a vacuum is applied to hold the wound dressing in place in afluid-tight seal around the periphery of the wound-facing face of thewound dressing, the wound dressing may be provided with a siliconeflange or lip to seal the dressing around the wound. This removes theneed for adhesives and associated trauma to the patient's skin.

Where the interior of, and the flow of irrigant and/or wound exudate toand through, the dressing is under any significant positive pressure,which will tend to act at peripheral points to lift and remove thedressing off the skin around the wound. In such use of the apparatus, itmay thus be necessary to provide means for forming and maintaining sucha seal or closure over the wound against such positive pressure on thewound, to act at peripheral points for this purpose. Examples of suchmeans include light switchable adhesives, as above, to secure thedressing in place to prevent leakage.

Since the adhesion of a light switchable adhesive is reduced byphotocuring, thereby reducing the trauma of removal of the dressing, afilm of a more aggressive adhesive may be used, e.g. on a flange, asabove. Examples of suitable fluid adhesives for use in more extremeconditions where trauma to the patient's skin is tolerable include onesthat consist essentially of cyanoacrylate and like tissue adhesives,applied around the edges of the wound and/or the proximal face of thebacking layer of the wound dressing, e.g. on a flange or lip.

Further suitable examples of such securing means include adhesive (e.g.with pressure-sensitive adhesive) and non-adhesive, and elastic andnon-elastic straps, bands, loops, strips, ties, bandages, e.g.compression bandages, sheets, covers, sleeves, jackets, sheathes, wraps,stockings and hose, e.g. elastic tubular hose or elastic tubularstockings that are a compressive fit over a limb wound to apply suitablepressure to it when the therapy is applied in this way; and inflatablecuffs, sleeves, jackets, trousers, sheathes, wraps, stockings and hosethat are a compressive fit over a limb wound to apply suitable pressureto it when the therapy is applied in this way.

Such securing means may each be laid out over the wound dressing toextend beyond the periphery of the backing layer of the wound dressing,and as appropriate will be adhered or otherwise secured to the skinaround the wound and/or itself and as appropriate will apply compression(e.g. with elastic bandages, stockings) to a degree that is sufficientto hold the wound dressing in place in a fluid-tight seal around theperiphery of the wound,

Such securing means may each be integral with the other components ofthe dressing, in particular the backing layer.

Alternatively, it may be permanently attached or releasably attached tothe dressing, in particular the backing layer, with an adhesive film,for example, or these components may be a Velcro™, push snap ortwist-lock fit with each other.

The securing means and the dressing may be separate structures,permanently unattached to each other.

In a more suitable layout for higher positive pressures on the wound, astiff flange or lip extends around the periphery of the proximal face ofthe backing layer of the wound dressing as hereinbefore defined.

The flange or lip is concave on its proximal face to define a peripheralchannel or conduit. It has a suction outlet that passes through theflange or lip to communicate with the channel or conduit and may beconnected to a device for applying a vacuum, such as a pump or a pipedsupply of vacuum. The backing layer may be integral with or attached,for example by heat-sealing, to the flange or lip extending around itsproximal face.

To form the relatively fluid-tight seal or closure over a wound that isneeded and to prevent passage of irrigant and/or exudate under theperiphery of the wound-facing face of the wound dressing, in use of theapparatus, the dressing is set on the skin around the wound.

The device then applies a vacuum to the interior of the flange or lip,thus forming and maintaining a seal or closure acting at peripheralpoints around the wound against the positive pressure on the wound.

With the foregoing means of attachment, and means for forming andmaintaining a seal or closure over the wound, against positive ornegative pressure on the wound at peripheral points around the wound,the wound dressing sealing periphery is preferably of a generally roundshape, such as an ellipse, and in particular circular.

In certain embodiments there is provided a conformable wound dressing,characterised in one embodiment in that it comprises a backing layerwith a wound-facing face which is capable of forming a relativelyfluid-tight seal or closure over a wound and has (a) at least one inletpipe for connection to a fluid supply tube, which passes through and/orunder the wound-facing face, and (b) at least one outlet pipe forconnection to a fluid offtake tube, which passes through and/or underthe wound-facing face, (c) the point at which the or each inlet pipe andthe or each outlet pipe passes through and/or under the wound-facingface forming a relatively fluid-tight seal or closure over the wound.

The dressing is advantageously provided for use in a bacteria-proofpouch.

The conformable wound dressing may be used for aspirating, irrigatingand/or cleansing wounds in conjunction with a biodegradable scaffold,which permits fluid supply towards the wound bed from the wounddressing.

The dressings depicted and described in WO 03/004647 may be used in theapparatus of certain embodiments of the present invention with means forsupplying thermal energy to the fluid in the wound, e.g. a conductiveheater, acting on the irrigant liquid in the flowpath upstream of thewound dressing, e.g. in the fluid supply tube from the irrigant fluidreservoir, usually as close to the wound dressing backing layer aspossible.

Embodiments of the present invention may also include: (a) a suctionhead having a first face; (b) a second face opposite said first face,wherein said second face is comprised of a plurality of projections,said projections defining a plurality of channels for facilitating flowof fluids to an opening in said second face and through said first face,wherein said opening is adapted for connection to a suction tube; and(c) a surgical drape having an aperture coincident said opening, saidsurgical drape extending over a region, and overlapping beyond theperimeter of said first face, and wherein said surgical drape comprisesa flexible adhesive coated film adhered to said region of said firstface and a release-coated backing extending over said second face andadhered to the overlapping portion of said surgical drape.

For distributing fluid across a wound surface, particular embodiments ofthe present invention may also include: (a) a suction head having afirst face; (b) a second face opposite said first face; (c) a pluralityof projections coincident from said second face, wherein saidprojections form a contact surface with the wound surface, and wherein aplurality of channels for facilitating flow of fluids are definedbetween said projections, said channels remaining out of contact withthe wound surface; and (d) an aperture in fluid communication with saidchannels formed by said projections and formed through said first faceand second face.

Embodiments of the present invention may also comprise: a method ofusing a therapeutic apparatus for stimulating the healing of wounds inmammals comprising the steps of: (a) inserting a porous pad into or onsaid wound such that said porous pad is in contact with said wound,wherein said porous pad has at least a partial outer surface and aninner body, said outer surface being adapted for contact with surface ofsaid wound with small first pores no larger than about 100 microns indiameter to enhance biocompatibility; (b) securing said porous paidwithin said wound with the dressing cover to maintain a negativepressure at the site of said wound; (c) generating a negative pressureat said wound through said porous pad; and (d) collecting fluids fromsaid wound through said porous pad.

Wound Filler

As also mentioned herein, the backing layer that is applied may be anythat is appropriate to the present system of therapy and permits apositive or negative pressure of up to 50% atm., more usually up to 25%atm. to be applied to the wound.

It is thus often a microbe-impermeable film, sheet or membrane, which issubstantially flat, depending on any pressure differential on it, andoften with a (generally uniform) thickness similar to such films orsheets used in conventional wound dressings, i.e. up to 100 micron,preferably up to 50 micron, more preferably up to 25 micron, and of 10micron minimum thickness.

The backing layer may often have a rigid and/or resiliently inflexibleor stiff area to resist any substantial play between other componentsthat are not mutually integral, and may be stiffened, reinforced orotherwise strengthened, e.g. by a projecting boss.

Such a form of dressing would not be very conformable to the scaffoldand/or wound bed, and may effectively form a chamber, hollow or cavitydefined by a backing layer and the scaffold and/or wound bed under thebacking layer.

It may be desirable that the interior of the wound dressing conform tothe scaffold and/or wound bed, even for a wound in a highly exudingstate. Accordingly, one form of the dressing is provided with a woundfiller under the backing layer. This is favourably a resilientlyflexible, e.g. elastomeric, and preferably soft, structure with goodconformability to wound shape. It is urged by its own resilience againstthe backing layer to apply gentle pressure on the scaffold and woundbed.

The wound filler may be integral with the other components of thedressing, in particular the backing layer. Alternatively, it may bepermanently attached to them/it, with an adhesive film, for example, orby heat-sealing, e.g. to a flange or lip extending from the proximalface, so a not to disrupt the relatively fluid-tight seal or closureover the wound that is needed.

Less usually, the wound filler is releasably attached to the backinglayer, with an adhesive film, for example, or these components may be apush, snap or twist-lock fit with each other. The wound filler and thebacking layer may be separate structures, permanently unattached to eachother.

The wound filler may be or comprise a solid integer, favourably aresiliently flexible, e.g. elastomeric, and preferably soft, structurewith good conformability to wound shape. Examples of suitable forms ofsuch wound fillers are foams formed of a suitable material, e.g. aresilient thermoplastic. Preferred materials for the fillers, or presentwound dressing, include reticulated filtration polyurethane foams withsmall apertures or pores. Alternatively or additionally, it may be inthe form of, or comprise one or more conformable hollow bodies definedby a film, sheet or membrane, such as a bag, chamber, pouch or otherstructure, filled with a fluid or solid that urges it to the woundshape.

The film, sheet or membrane, often has a (generally uniform) thicknesssimilar to that of films or sheets used in conventional wound dressingbacking layers. That is, up to 100 micron, preferably up to 50 micron,more preferably up to 25 micron, and of 10 micron minimum thickness, andis often resiliently flexible, e.g. elastomeric, and preferably soft.Such a filler is often integral with the other components of thedressing, in particular the backing layer, or permanently attached tothem/it, with an adhesive film, for example, or by heat-sealing, e.g. toa flange

Examples of suitable fluids contained in the hollow body or bodiesdefined by a film, sheet or membrane include gases, such as air,nitrogen and argon, more usually air, at a small positive pressure aboveatmospheric; and liquids, such as water, saline. Examples also includegels, such as silicone gels, e.g. CaviCare™ gel, or preferablycellulosic gels, for example hydrophilic cross-linked cellulosic gels,such as Intrasite™ cross-linked materials. Examples also include aerosolfoams, where the gaseous phase of the aerosol system is air or an inertgas, such as nitrogen or argon, more usually air, at a small positivepressure above atmospheric; and solid particulates, such as plasticscrumbs.

In an alternative embodiment the filler of the apparatus canconveniently be an expandable or contractible module which is the meansto apply stress to the wound bed. In one preferred embodiment the modulecomprises an inflatable body, e.g. an inflatable pouch or bag. Ofcourse, if the backing layer is a sufficiently conformable and/or e.g.an upwardly dished sheet, the backing layer may lie under the woundfiller, rather than vice versa.

In this type of layout, in order for the wound filler to urge the wounddressing towards the scaffold and wound bed, it will usually have to befirmly adhered or otherwise releasably attached to the skin around thewound. This is especially the case in those embodiments where the woundfiller and the backing layer are separate structures, permanentlyunattached to each other.

In such a layout for deeper wounds when the therapy is applied in thisway, the means for such attachment may also form and maintain a seal orclosure over the wound. Where the filler is over the backing layer, andthe fluid inlet pipe(s) and outlet pipe(s) pass through the wound-facingface of the backing layer, they may run through or around the woundfiller over the backing layer.

One form of the dressing is provided with a wound filler under thebacking layer that is or comprises a resiliently flexible, e.g.elastomeric, and preferably soft, hollow body defined by a film, sheetor membrane, such as a bag, chamber, pouch or other structure. It hasapertures, holes, openings, orifices, slits or slots, or tubes, pipes,tubules or nozzles. It communicates with at least one inlet or outletpipe through at least one aperture, hole, opening, orifice, slit orslot.

The fluid contained in the hollow body may then be the aspirating orirrigating fluid in the apparatus. The hollow body or each of the hollowbodies then effectively forms an inlet pipe or outlet pipe manifold thatdelivers the aspirating fluid directly to the scaffold and wound bed orcollects the fluid directly from the wound respectively via the holes,openings, orifices, slits or slots, or the tubes, pipes or hoses, etc.in the film, sheet or membrane.

When the therapy is applied in this way, the type of the filler may alsobe largely determined by the depth and/or capacity of the wound.

Thus, for shallower wounds, examples of suitable wound fillers as acomponent of a wound dressing include ones that consist essentially ofone or more conformable hollow bodies defining an inlet pipe and/oroutlet pipe manifold that delivers the aspirating fluid directly to thescaffold and wound bed or collects the fluid directly from the wound.

A more suitable wound filler for deeper wounds when the therapy isapplied in this way may be one which comprises one or more conformablehollow bodies defined by, for example a polymer film, sheet or membrane,that at least partly surround(s) a solid integer. This may provide asystem with better rigidity for convenient handling.

The wound filler under the backing layer may effectively form an inletpipe or outlet pipe manifold. If not, in order for aspiration and/orirrigation of the wound bed to occur, it is appropriate for one or morebores, channels, conduits, passages, pipes, tubes, tubules and/orspaces, etc. to run from the point at which the fluid inlet pipe(s) andoutlet pipe(s) pass through and/or under the wound-facing face of thebacking layer through or around the wound filler under the backinglayer.

Less usually, the wound filler is an open-cell foam with pores that mayform such bores, channels, conduits, passages and/or spaces through thewound filler under the backing layer.

Where the filler is or comprises one or more conformable hollow bodiesdefined by, for example a polymer film, sheet or membrane, it may beprovided with means for admitting fluids to the scaffold and wound bedunder the wound dressing.

These may be in the form of pipes, tubes, tubules or nozzles runningfrom the point at which the fluid inlet pipe(s) and outlet pipe(s) passthrough and/or under the wound-facing face of the backing layer throughor around the wound filler under the backing layer.

All of the suitable layouts for shallower wounds that compriseblind-bore, perforated inlet pipe or outlet pipe manifolds that aspiratefluid in the wound when the dressing is in use, that are describedhereinbefore, may be used under a wound filler under the backing layer.

In brief, suitable layouts include ones where one or both manifolds are(a) annular or toroidal (regular, e.g. elliptical or circular orirregular), optionally with blind-bore, perforated radial tubes, pipesor nozzles, branching from the annulus or torus; and/or (b) in ameandering, tortuous, winding, zigzag, serpentine or boustrophedic (i.e.in the manner of a ploughed furrow) pattern, or (c) defined by slots inand apertures through layers attached to each other in a stack.

Inlet and Outlet Pipes

The apparatus for aspirating, irrigating, and/or cleansing comprisesinlet and outlet pipes, or tubes, which carry the irrigating fluid tothe wound and the aspirating fluid away from the wound.

The inlet and/or outlet tubes, the fluid tube and the fluid supply tube,etc. may be of conventional type, e.g. of elliptical or circularcross-section, and may suitably have a uniform cylindrical bore,channel, conduit or passage throughout their length, and suitably thelargest cross-dimension of the bore may be up to 10 mm for large torsowounds, and up to 2 mm for limb wounds.

The tube walls should be suitably thick enough to withstand any positiveor negative pressure on them, in particular if the volume of irrigantand/or wound exudate from the wound in is increased by continuingaddition to it of wound exudate, and/or fluid passing from a cleansingfluid through a selectively permeable integer, for example the polymerfilm, sheet or membrane of a two-phase system, such as an aspiration andirrigation unit. However, the prime purpose of such tubes is to conveyfluid irrigant and exudate through the length of the apparatus flowpath, rather than to act as pressure vessels.

The tube walls may suitably be at least 25 micron thick. The bore or anyperforations, apertures, holes, openings, orifices, slits or slots alongthe pipes, etc. or in the hollow body or each of the hollow bodies maybe of small cross-dimension. They may then effectively form amacroscopic and/or microscopic filter for particulates including celldebris and micro-organisms, whilst allowing proteins and nutrients topass through. Such tubes, pipes or hoses, etc. through and/or around thefiller, whether the latter is a solid integer and/or one or moreresiliently flexible or conformable hollow bodies, are described infurther detail hereinbefore in connection with the inlet pipe(s) andoutlet pipe(s). The whole length of the apparatus for aspirating,irrigating, and/or cleansing wounds should be microbe-impermeable oncethe wound dressing is over the wound in use.

To form the relatively fluid-tight seal or closure over a wound andaround the inlet pipe(s) and outlet pipe(s) at the point at which theypass through and/or under the wound-facing face, the backing layer maybe integral with these other components.

The components may alternatively just be a push, snap or twist-lock fitwith each other, or adhered or heat-sealed together.

The or each inlet pipe or outlet pipe may be in the form of an aperture,such as a funnel, hole, opening, orifice, luer, slot or port forconnection as a female member respectively to a mating end of (a) afluid tube and/or fluid supply tube (optionally or as necessary viameans for forming a tube, pipe or hose, or nozzle, hole, opening,orifice, luer, slot or port for connection as a male member respectivelyto a mating end of (b) a fluid tube and/or fluid supply tube (optionallyor as necessary via means for supply flow regulation) or (c) a fluidofftake tube.

Where the components are integral they will usually be made of the samematerial (for which it will be understood that materials that are listedabove are amongst those that are suitable).

Where, alternatively, they are a push, snap or twist-lock fit, the maybe of the same material or of different materials. In either case,materials that are listed above are amongst those that are suitable forall the components.

The or each pipe will generally pass through, rather than under thebacking layer. In such case, the backing layer may often have a rigidand/or resiliently inflexible or stiff area to resist any substantialplay between the or each pipe and the or each mating tube, ordeformation under pressure in any direction.

It may often be stiffened, reinforced or otherwise strengthened by aboss projecting distally (outwardly from the wound) around each relevanttube, pipe or hose, or nozzle, hole, opening, orifice, luer, slot orport for connection to a mating end of a fluid tube and/or fluid supplytube or fluid offtake tube.

Alternatively or additionally, where appropriate the backing layer mayhave a stiff flange or lip extending around the proximal face of thebacking layer to stiffen, reinforce or otherwise strengthen the backinglayer. The wound dressing may not comprise any integer under the backinglayer in the wound in use, other than the scaffold mentioned herein.

Where a simple pipe is used to supply the irrigant to the wound, thismay not provide a system to distribute irrigant over a sufficientfunctional surface area to irrigate the wound at a practical rate to besuitable for use, in particular in chronic wound aspiration andirrigation, with relatively high concentrations of materials that aredeleterious to wound healing.

It may be advantageous to provide a system where wound irrigant may bedistributed more evenly, or pass in a more convoluted path under thedressing over the wound bed and/or scaffold.

Accordingly, one form of the dressing is provided with a ‘tree’ form ofpipes, tubes or tubules that radiate from an inlet manifold to the woundbed and/or scaffold to end in apertures and deliver the aspirating fluiddirectly to the scaffold and wound bed via the apertures. Similarly,there is optionally an outlet manifold from which tubules radiate andrun to the wound bed and/or scaffold to end in openings and collect thefluid directly from the wound bed.

The pipes, etc. may radiate regularly or irregularly through the woundin use, respectively from the inlet or outlet manifold, althoughregularly may be preferred. A more suitable layout for deeper wounds isone in which the pipes, etc. radiate hemispherically and concentrically,to the wound bed and/or scaffold.

For shallower wounds, examples of suitable forms of such layout of thepipes, etc. include ones in which the pipes, etc. radiate in a flattenedhemiellipsoid and concentrically, to the wound bed and/or scaffold.

Other suitable forms of layout of the pipes, etc. include one which havepipes, tubes or tubules extending from the inlet pipe(s) and/or outletpipe(s) at the point at which they pass through and/or under thewound-facing face of the backing layer to run over the wound bed and/orscaffold. These may have a blind bore with perforations, apertures,holes, openings, orifices, slits or slots along the pipes, etc.

These pipes, etc. then effectively form an inlet pipe manifold thatdelivers the aspirating fluid directly to the scaffold and wound bed oroutlet pipe or collects the fluid directly from the wound respectively.It does so via the holes, openings, orifices, slits or slots in thetubes, pipes, tubules, etc. over most of the wound bed and/or scaffoldunder the backing layer.

It may be desirable that the tubes, pipes or tubules are resilientlyflexible, e.g. elastomeric, and preferably soft, structures with goodconformability in the wound and the interior of the wound dressing.

When the therapy is applied in this way, the layout of the tubes, pipes,tubules, etc. may depend on the depth and/or capacity of the wound.Thus, for shallower wounds, examples of suitable forms of such layout ofthe tubes, pipes, tubules, etc. include ones that consist essentially ofone or more of the tubes, etc in a spiral.

A more suitable layout for deeper wounds when the therapy is applied inthis way may be one which comprises one or more of the tubes, etc in ahelix or spiral helix. Other suitable layouts for shallower woundsinclude one which have blind-bore, perforated inlet pipe or outlet pipemanifolds that aspirate fluid in the wound when the dressing is in use.One or both of these may be such a form, the other may be, e.g. one ormore straight blind-bore, perforated radial tubes, pipes or nozzles.

A preferred form of inlet pipe (or less usually) outlet pipe manifoldthat delivers the aspirating fluid directly to the scaffold and woundbed or collects the fluid directly from the wound respectively is onethat comprise one or more conformable hollow bodies defined by a film,sheet or membrane, such as a bag, chamber, pouch or other structure,filled with the irrigant (or less usually) aspirate from the wound,passing through perforations, apertures, holes, openings, orifices,slits or slots in the film, sheet or membrane defining the hollow bodyor hollow bodies.

These may be of small cross-dimension, so that they may then effectivelyform microperforations, microapertures or pores in a permeable integer,for example the polymer film, sheet or membrane.

This type of manifold for irrigation (more usually) provides the highestuniformity in the flow distribution of irrigant over the wound at apractical rate to be suitable for use, in particular in chronic woundaspiration and irrigation, and hence to provide a system where materialsthat are beneficial in promoting wound healing, from cells or tissue,such as growth factors, cell matrix components, extracellular cellmatrix components and fragments thereof, and other physiologicallyactive components of the exudate from a wound, are distributed moreevenly under the dressing over the wound bed.

This type of manifold for irrigation (more usually) is also capable ofacting as a wound filler, and is noted below with regard to woundfillers under the backing layer, since it is a resiliently flexible,e.g. elastomeric, and soft, structure with good conformability to woundshape.

It is urged by its own resilience against the backing layer to applygentle pressure on the scaffold and wound bed, and is therefore alsocapable of acting as a wound filler. The film, sheet or membrane, oftenhas a (generally uniform) thickness similar to that of films or sheetsused in conventional wound dressing backing layers.

Another suitable layout is one in which (a) an inlet pipe and/or outletpipe manifold that delivers the aspirating fluid directly to thescaffold and wound bed or collects the fluid directly from the woundrespectively (b) via inlet and/or outlet tubes, pipes or tubules, (c)and the inlet manifold and/or outlet manifold is formed by slots inlayers permanently attached to each other in a stack, and (d) the inletand/or outlet tubes, pipes or tubules are formed by apertures throughlayers permanently attached to each other in a stack. (In FIG. 10a thereis shown an exploded isometric view of such a stack, which isnon-limiting.)

Sterilization, Buffering, and Anti-Deposition

It is desirable that the wound dressing and the interior of theapparatus for aspirating, irrigating, and/or cleansing wounds issterile.

The fluid may be sterilized in the fluid reservoir and/or the rest ofthe system in which the fluid moves by ultraviolet, gamma or electronbeam irradiation (except for the integer that contains the tissue orcell component, since this may adversely affect the viability andactivity of the cells). This way, in particular reduces or eliminatescontact of internal surfaces and the fluid with any sterilizing agent.

Examples of other methods of sterilization of the fluid also includee.g. the use of (a) ultrafiltration through microapertures ormicropores, e.g. of 0.22 to 0.45 micron maximum cross-dimension, to beselectively impermeable to microbes; and (b) fluid antiseptics, such assolutions of chemicals, such as chlorhexidine and povidone iodine; metalion sources, such as silver salts, e.g. silver nitrate; and hydrogenperoxide; (c) although the latter involve contact of internal surfacesand the fluid with the sterilizing agent.

It may be desirable that the interior of the wound dressing, the rest ofthe system in which the fluid moves, and/or the scaffold and wound bed,even for a wound in a highly exuding state, are kept sterile after thefluid is sterilized in the fluid reservoir, or that at least naturallyoccurring microbial growth is inhibited. Thus, materials that arepotentially or actually beneficial in this respect may be added to theirrigant initially, and as desired the amount in increased by continuingaddition.

Examples of such materials include antibacterial agents (some of whichare listed above), and antifungal agents. Amongst those that aresuitable are, for example triclosan, iodine, metronidazole, cetrimide,chlorhexidine acetate, sodium undecylenate, chlorhexidine and iodine.

Buffering agents, such as potassium dihydrogen phosphate/disodiumhydrogen phosphate. may be added to adjust the pH, as may localanalgesics/anaesthetics, such as lidocaine/lignocaine hydrochloride,xylocaine (adrenoline, lidocaine) and/or anti-inflammatories, to reducewound pain or inflammation or pain associated with the dressing.

In order to combat the deposition of materials in the flow path from theirrigant, a repellent coating may be used at any point or on any integerin the path in direct contact with the fluid, e.g. on the means forproviding simultaneous aspiration and irrigation of the wound or anydesired tube or pipe.

Examples of coating materials for surfaces over which the aspiratingfluid passes include (a) anticoagulants, such as heparin, and (b) highsurface tension materials, such as PTFE, and polyamides, (c) which areuseful for growth factors, enzymes and other proteins and derivatives.

Thermal Energy

In certain embodiments, the apparatus further for aspirating, irrigatingand/or cleansing wounds further comprises a means for supplying thermalenergy to the fluid in the wound. Examples of means for supplyingthermal energy to the fluid in the wound include as may be appropriateconducted thermal energy, electromagnetic radiation of an appropriatewavelength, or (less often) as convected thermal energy. In the presentapparatus, heat will usually be conducted to the wound bed by theirrigant and/or wound exudate within the dressing. However, thermalenergy may as appropriate be supplied to the irrigant and/or woundexudate within the dressing, and may be applied to the fluid by anysuitable means, at any suitable point, often depending on particularcomponents and/or materials that are used.

Examples of such means include: (a) direct conductive contact of theirrigant and/or wound exudate with a heater and/or conductively heatedcomponent of the apparatus flow path; (b) direct electromagneticirradiation at an appropriate wavelength, e.g. infrared and/or nearinfrared from a radiative heater of the irrigant fluid and/or woundexudate; and/or (c) electromagnetic irradiation from a radiative heaterof a component of the apparatus flow path that absorbs electromagneticirradiation at an appropriate wavelength, e.g. infrared and/or nearinfrared and is in direct conductive contact with the irrigant and/orwound exudate.

Accordingly, one embodiment of the present apparatus for irrigating,supplying thermal energy to and cleansing wounds supplying thermalenergy to and cleansing wounds is characterised in that it comprisesmeans for providing and conducting thermal energy to the fluid in thewound.

Another embodiment of the present apparatus for irrigating, supplyingthermal energy to and cleansing wounds is characterised in that itcomprises means for supplying electromagnetic radiation of anappropriate wavelength to the fluid in the wound.

Another embodiment of the present apparatus for irrigating, supplyingthermal energy to and cleansing wounds is characterised in that itcomprises means for supplying electromagnetic radiation of anappropriate wavelength to the fluid in the wound.

The heater of the irrigant fluid and/or wound exudate and/or heatedcomponent of the apparatus flow path may be at any convenient orappropriate position or component of the apparatus flow path. Examplesinclude a heater and/or conductively heated component of the apparatusflow path upstream of any outlet pipe(s) that pass through and/or underthe wound-facing face of the backing layer of the wound dressing, (a)mounted distally of the body on, in or inside of the dressing; (b)mounted in, on, at or near one or more of the fluid inlet pipe(s); (c)mounted in, on, at or near one or more of the connectors in the tubesthat form the flow path of the apparatus; and/or (d) mounted in, on, ator near the reservoir.

As noted above, the irrigant and/or wound exudate fluid in the interiorof the wound dressing is beneficially maintained at a temperature thatis at or near the temperature naturally occurring in the relevant bodilypart and/or normothermic temperature. The desired or optimum temperatureof the wound will substantially determine (a) the position along theapparatus flow path or the component of the apparatus flow path wherethe heater and/or conductively heated component of the apparatus flowpath is mounted relative to the dressing; (b) the flow rate of irrigantfluid and/or wound exudate; (c) the temperature to which the point ofsupply of thermal energy to apparatus is raised; (d) the thermalinsulation of the system in which the fluid moves and heat is conductedto the wound; and/or (e) the nature of the heater.

In examples of direct conductive contact of the irrigant and/or woundexudate with a heater and/or conductively heated component of theapparatus flow path, the heater may be or be connected to a heatexchanger mounted in conductive contact with irrigant and/or woundexudate at an appropriate point in the system in which the fluid movesand heat is conducted to the wound. The heat exchanger may comprise anarray of thermally conductive extended surfaces, such as fins, bafflesor other like structures of conductive material in a more convolutedform with a relatively large surface area and which transfer thermalenergy when a temperature drop is applied over them, mounted inconductive contact with irrigant and/or wound exudate, with spacestherebetween such that wound irrigant and/or wound exudate may movethrough the spaces.

Alternatively, where appropriate it may be provided in the form of alike array of conductive hollow structures, such as pipes, tubes orother like structures in the apparatus flow path, through which a heatexchanger fluid moves and transfers heat from a heat source to beconducted to the wound). The array of conductive hollow structures mayconsist essentially of small apertures or pores that may form suchbores, channels, conduits and/or passages through a heated metal sinter,such as one of e.g. stainless steel. This is mounted in conductivecontact with irrigant and/or wound exudate in the apparatus flow path,through which the fluid moves, so that heat is conducted to the wound.Such a heat exchanger may be outside the wound space and the backinglayer or within the wound space and under the backing layer. If it isoutside the wound space and the backing layer, it is preferably as closeto the wound dressing backing layer as possible.

Examples of conductive heaters include:

(a) an electric heater mounted in conductive contact with irrigantand/or wound exudate (but electrically insulated from the fluid and thesystem in which the fluid moves and heat is conducted to the wound). Theheater may inter alia comprise:

(i) an array of electrically resistive but conductive wires, fibres,filaments, strands or other like structures that generate thermal energywhen a voltage drop is applied over them. The array may be a parallelarray with spaces therebetween, and the wound irrigant and/or woundexudate may move through the spaces. Alternatively, where appropriate itmay be provided in the form of non-woven or woven fabric, such as awoven layer or sheet. This may as appropriate be used essentially as aflat sheet or membrane of material in a more convoluted form, e.g.conformed to the form of other structures such as pipes, tubes, etc. inthe apparatus flow path, as a duct, sheath, or casing, or other likestructure. Depending on any pressure differential across it may requireother materials on or in it to stiffen, reinforce or otherwisestrengthen it. The material of the heater may have a positive or (lesspreferably) a negative thermal coefficient of resistance. A controlfeedback circuit is needed with a negative coefficient of resistance fortemperature regulation.

Materials that are described by way of example herein to be suitable foruse in certain embodiments of the present invention will be capable ofthis function. Depending on other components and/or materials that arepresent, examples of suitable materials include carbon fibres andfabric, such as a woven layer or sheet, which may as appropriate be madeessentially of carbonised acrylate, such as polyacrylonitrile andcopolymers thereof.

(ii) an electrically insulating flat sheet or membrane substrate thathas sites on its surface that are connected by an array of electricallyresistive but conductive tracks, traces, outlines, or other likestructures, e.g. filled channels, conduit and the like, and, e.g. etchedfoil, which generate thermal energy when a voltage drop is applied overthem. The array may be a parallel array with spaces therebetween,connected together at each end, or comprise or consist essentially ofone or more such integers in a spiral, or in a meandering, tortuous,winding, zigzag, serpentine or boustrophedic (i.e. in the manner of aploughed furrow) pattern. Examples of suitable materials for the arrayof electrically resistive but conductive tracks, traces, outlines, orother like structures include carbon and/or metals, such as Thermion™, anickel-coated non-woven carbon fabric and resistance heating alloys,such as Kanthal™, Alkrothal™, Nikrothal™, and Nifethal™. For theelectrically insulating flat sheet or membrane substrate, suitablematerials include PTFE, polyamides, and (i) materials such as aromaticpolysulphones, polyethersulphones, polyetherether-sulphones,polyketones, polyetherketones; and polyetherether-ketones, andsulphonated derivatives thereof, and mixtures thereof; and (ii) expoxyresins. The array of electrically resistive but conductive tracks,traces, outlines, or other like structures, may be generated by etchingor engraving, e.g. with electron beam irradiation and/or with fluidchemicals. Alternatively, where appropriate it may be provided byprinting, imprinting, stamping or vapour deposition of conventionaltype.

(iii) an array of electrically resistive but conductive, mutuallyconnected thermocouples that are potentially capable of generatingthermal energy by the Peltier effect when a voltage drop is applied overthem. The array may be a parallel array with spaces therebetween, andthe wound irrigant and/or wound exudate may move through the spaces.Alternatively, it may be permanently or releasably attached to thesurface of a substrate of the type described by way of example under ii)as suitable for use in certain embodiments of the present invention.Depending on other components and/or materials that are present,examples of suitable materials include thermoelectric modules comprisingpellets of bismuth telluride doped with selenium and antimony ofdifferent conductivity, the thermocouple pairs being connected in seriesand sandwiched between ceramic substrates. In the Peltier effect when avoltage drop is applied over a thermocouple, one part potentiallyundergoes heating, and can thus supply thermal energy to the woundthrough a heat transfer medium (the irrigant). The other part undergoescooling and can thus act as a thermal pump from the ambient to the fluidirrigant and exudate in the apparatus flow path to the wound. However,thermal energy transfer in this highly controllable manner requiresorientation of the thermocouple array such that the side capable ofgaining thermal energy by the Peltier effect is in conductive contactwith the irrigant and/or wound exudate. Examples of (a) (i) & (ii)include a foam reservoir dressing, such as Allevyn(™, Smith & Nephew)and Tielle(™, Johnson & Johnson), having an electrical heater, mounteddistally of the body on it.

(b) an inductive heater element mounted in conductive contact withirrigant and/or wound exudate (but electrically insulated from the fluidand the system in which the fluid moves and heat is conducted to thewound). The heater may inter alia comprises a piece of ferromagneticmaterial, such as magnetic stainless steel in conductive contact withirrigant and/or wound exudate, and an inductive source that will beadjacent (but not necessarily attached) to the dressing in use, but mayotherwise be remote from the wound). Examples of the latter include aferromagnetic coil, spiral, helix or spiral helix, or loop or a moreconvoluted form, e.g. a meandering, tortuous, winding, zigzag,serpentine or boustrophedic (i.e. in the manner of a ploughed furrow)pattern, in particular in one plane, of an inductive often highlyconductive material, connected to an alternating electrical potentialsource. This is potentially capable of generating thermal energy in thecore when a varying potential is applied to the coil, spiral or spiralhelix, or loop or a more convoluted form. This is often at mains voltageand frequency at the location where the device is used, though a rangeof either may be used.

(c) a heater mounted in conductive contact with irrigant and/or woundexudate to which it transfers thermal energy to the fluid inrecirculation from a heat source within it, which is a fuel cell. Inthis, atmospheric oxygen and/or other molecules oxidise one or morespecies of fuel molecules, often in a catalytic bed. Examples of fuelmaterials that have a strong oxidation exotherm include gases, where thegaseous phase of the aerosol system is air and a fuel gas, such ashydrogen or an alkane, such as methane, ethane and butane. The catalystis often solid particulates, such as composites of copper and rare earthoxides, such as optionally samaria doped ceria, comprised in acrystalline material for convenient handling; or platinum powder coatedonto carbon paper or cloth.

(d) a heater mounted in conductive contact with irrigant and/or woundexudate to which it transfers thermal energy to the fluid inrecirculation from a heat source within it, which is a material thatundergoes a highly exothermal phase change. Examples of (d) include

(i) a heater containing materials that undergo a highly exothermalcrystallisation or solidification phase change, such as supersaturatedsolutions of chemicals, such as metal ion salts. Sodium thiosulphate isa source of a strong crystallisation exotherm, as is sodium acetatesolution. The fluid or solid material is often comprised in one or moreconformable hollow bodies. These may be defined by, for example apolymer film, sheet or membrane, such as a bag, chamber, pouch or otherstructure, of the backing layer, e.g. of polymer film, for convenienthandling. In the case where the heat source is in the form of acrystallisation system, such as one based on sodium thiosulphate, thebag, chamber, pouch or other structure is often provided with a sourceof mechanical shock that is appropriate for inducing crystallisation.Examples include a catastrophically resiliently flexible or stiff metalbutton, such as one of e.g. aluminium or stainless steel. Such heatersare less preferred than an electrical heater, since electrical heatingcan give constant heating intensities in a highly controllable manner.In contrast, a strong crystallisation or solidification exotherm is lesscontrollable or constant.

(ii) a heater containing materials that undergo an exothermalcondensation phase change, i.e. from gaseous or volatile products, suchas the Freon hydrocarbon series to liquids. Preferred materials include,in particular those that condense at or near normothermic temperature.Such a heater of the irrigant fluid and/or wound exudate may be operatedas a heat pump that absorbs thermal energy, e.g. from the environment ofa component of the apparatus flow path into the component of theapparatus flow path. In examples of (a) direct electromagneticirradiation at an appropriate wavelength, e.g. infrared and/or nearinfrared from a radiative heater of the irrigant fluid and/or woundexudate; and/or (b) electromagnetic irradiation from a radiative heaterof a component of the apparatus flow path that absorbs electromagneticirradiation at an appropriate wavelength, e.g. infrared and/or nearinfrared and is in direct conductive contact with the irrigant and/orwound exudate. The heater usually works at such temperatures as willdeliver 34 to 55° C., preferably 35 to 42° C., and optimally 36 to 38°C. at the wound bed. Examples of sources of direct or indirectelectromagnetic irradiation of the irrigant fluid and/or wound exudateat an appropriate wavelength include infrared and/or near infrared froma radiative heater. In the apparatus the type and materials of theheater will be largely determined by its specific function and thewavelengths and intensities to be applied to the fluid within the farinfrared, mid infrared or near infrared spectrum, and its position inthe apparatus. Examples of suitable wavelengths to apply to the fluidinclude: (a) for the far infrared, 4 to 1000 micrometre, (b) for the midinfrared, 1.4 to 4 micrometre, and (c) for the near infrared, 0.75 to1.5 micrometre. Examples of suitable levels of intensity include thoseconventionally used in medical applications and known to the skilledperson. The higher end of these ranges are potentially more suitable forhospital use, where relatively high intensity infrared or near infraredirradiation at relevant wavelengths may be used safely underprofessional supervision. Such a device may also suitably be one that iscapable of pulsed, continuous, variable, and/or automated and/orprogrammable operation. Examples include:

(i) a radiative heater that is an incandescent filament lamp, light orother like structure, which is a source of radiation at relevantwavelengths to be applied to the fluid, e.g. infrared or near infraredirradiation. Examples of (i) include a heater that is a small infraredlamp, mounted on an infra-red transparent dressing backing layer;

(ii) a radiative heater that is a high-thermal energy, high-intensityLED (light emitting diode) or other like structure, which is a source ofradiation at relevant wavelengths to be applied to the fluid, e.g.infrared or near infrared irradiation; and

(iii) a radiative heater that is a high-thermal energy, high-intensitysource of radiation at relevant wavelengths to be applied to the fluid,e.g. infrared or near infrared irradiation. The type and materials ofthe heater will be largely determined by its specific function and thewavelengths and intensities to be applied to the fluid within thespectrum, and its position in the apparatus.

(e) Any r.f. and/or microwave frequency signal generator may be usedprovided temperatures at the wound do not exceed 38 to 40° C., andoptimally 36 to 38° C. Examples of sources of direct or indirectelectromagnetic irradiation of the irrigant fluid and/or wound exudateat an appropriate wavelength also include radio-frequency e.m.r. in arange of 3 to 300 MHz, such as 10 to 100 MHz, such as 20 to 50 MHz.Examples of preferred frequencies include microwave frequencies, using amicrowave magnetron, in a range such as 1 to 300 GHz, such as 1 to 100GHz, e.g. 1 to 50 GHz. It will be appreciated that at these frequencies,in the range of microwave frequencies in particular, thermal energy isnot just transferred to the fluid by simply being absorbed by the fluidand conducted to the wound. It is induced in the molecules in the fluidin the wound by radiation at an optimum frequency for such materials.

In all the above radiative heaters of the irrigant fluid and/or woundexudate, the electromagnetic irradiation from a radiative heater maypass into the fluid in the flow path directly, usually through a‘window’ that is transparent to the relevant wavelengths to be appliedto the fluid.

Amongst those materials that are suitable are glass; carbon fibres(which may be in a parallel array with spaces therebetween) and carbonfabric, such as a woven layer or sheet. This may as appropriate be madeessentially of carbonised acrylate, such as polyacrylonitrile andcopolymers thereof; and various well-known polymers.

The transmissive structures may, alternatively or additionally,effectively be in the form of optical fibre(s) or waveguides ofconventional type, e.g. (a) a tube, pipe, duct, fibre, filament, strandor other like structure, e.g. of carbon or the materials mentionedabove, which is transparent to the relevant wavelengths to be applied tothe fluid, (b) coated, enclosed or enveloped by a coating, layer, sheet,skin or concentric tube, pipe, duct, sheath, or casing, or other likestructure, of material on its outer face that is opaque and reflectiveto the relevant wavelengths.

These may pass at any relevant position along the apparatus flow pathinto the apparatus flow path where the heat is desired to be applied. Inone embodiment, they will pass under and/or through the backing layer ofthe dressing. The transmissive structures may effectively be in the formof optical fibre(s) formed by (a) at least one inlet pipe and/or fluidsupply tube and/or and/or at least one outlet pipe and/or fluid offtaketube, which passes through and/or under the wound-facing face, and istransparent or translucent to the relevant wavelengths to be applied tothe fluid in the wound, and preferably to those that are optimum forwound healing, (b) coated, enclosed or enveloped by a coating, layer,sheet, skin or concentric tube, pipe, duct, sheath, or casing, or otherlike structure, of material on its outer face that is opaque andreflective to the relevant wavelengths. An advantage of such wounddressings is that these optical fibres may also serve as diagnostic‘keyholes’ into the dressing to the wound bed in order to inspect thewound and assess its status. This is a significant advantage, inparticular in chronic wounds.

As noted above, radiative energy may be absorbed by a component of theapparatus flow path that absorbs electromagnetic irradiation at anappropriate wavelength, e.g. infrared and/or near infrared and is indirect conductive contact with the irrigant and/or wound exudate. Thus aradiative heater may be radiatively connected to a component of theapparatus flow path that absorbs electromagnetic irradiation at anappropriate wavelength, e.g. infrared and/or near infrared and is indirect conductive contact with the irrigant and/or wound exudate, e.g.by an air gap, the component containing a suitable absorbent andtransmissive structure, e.g. an aqueous fluid, such as a hydrogel, thatconducts heat through it to the irrigant fluid.

The temperature of the wound under the wound-facing face of the backinglayer of the wound dressing is generally held at a desired level, oftenthat for optimum performance of the wound healing process, such as atemperature found in the relevant bodily part, often within a range oftemperatures such as 34 to 55° C., preferably 35 to 42° C., andoptimally 36 to 38° C. at the wound bed. The temperature of the woundunder the wound-facing face of the backing layer of the wound dressingis generally held at a constant level throughout the desired length oftherapy, but may be varied cyclically in a desired regime.

However, the temperatures noted above, which are at or near thetemperature naturally occurring in the relevant bodily part may notprovide a system for optimum performance of the wound healing process.It may be desirable that the interior of the wound dressing is morebeneficially maintained at a temperature that degrades such molecules inthe fluid in the wound, e.g. an appropriate optimum degradationtemperatures for such materials, rather than at normothermictemperature. This may be the case in particular in chronic wounds, withrelatively high concentrations of materials that are deleterious towound healing. Other molecules involved in wound processes that aredetrimental to wound healing include or gaseous or volatile by-products,such as carbon dioxide. The irrigant may be warmed to a temperature thattends to degrade and/or outgas such molecules. The degradation oroutgassing temperature of each detrimental gas, such as carbon dioxide,in aqueous media is either known or may readily be calculated.

Accordingly, another type of this apparatus for irrigating, supplyingthermal energy to and cleansing wounds is provided with means formaintaining the wound at or near a temperature that is deleterious tomolecules that are detrimental to wound healing. As noted above, otherphysiologically active components of the wound cells are beneficial inpromoting wound healing and may be stimulated by radiation on the woundunder the backing layer. Where these are enzymes, growth factors andanti-inflammatories, cell mitochondria and other physiologically activecomponents of the exudate from a wound, examples of suitable wavelengthsand intensities to apply to the fluid in the wound to favour suchmaterials an cell components will be known to the skilled person.

Additionally, it is easy to avoid overheating of the wound and/orsurrounding surfaces, especially by electrical heating, since theheating must always pass to the wound through a heat transfer medium(the irrigant). This eliminates direct contact of the wound bed with theheater, and irrigant may be used as a heat transfer medium in a highlycontrollable manner.

The apparatus is most favourable to the wound healing process in chronicwounds, and thus for irrigating, and/or cleansing wounds such asdiabetic foot ulcers, and especially decubitus pressure ulcers.

In a preferred mode, certain embodiments of the present invention areused to provide a system of therapy which conveniently cleanses wounds,but also maintains them at or near normothermic temperature. Accordinglya preferred type of the apparatus for irrigating, and/or cleansingwounds is provided with means for maintaining the wound at or nearnormothermic temperatures.

As noted above, the apparatus for irrigating, and/or cleansing woundshas a direct effect on active components of fluid in contact with thewound, in particular solutes or disperse phase species that arebeneficial in promoting wound healing that are in contact with the woundbed. Additionally, cell mitochondria aid proliferation and hence woundhealing, in particular in chronic wounds, and are stimulated by nearinfrared radiation. Application of such radiation to the wound resultingin an increase in cell proliferation in the tissue underlying to thewound, and in the breaking strength of the new tissue. Otherphysiologically active components of the cells in the tissue underlyingthe wound that are beneficial in promoting wound healing may also bestimulated by radiation on the wound.

Physiologically Active Materials

The apparatus for aspirating, irrigating, and/or cleansing wounds may,in certain embodiments, further comprise means for supplyingphysiologically cative materials to the wound. The present form ofaspiration and/or irrigation therapy systems also often create a woundenvironment for better distribution of materials that are beneficial insome therapeutic aspect, in particular to wound healing, that arepresent in a wound, but may not be well distributed in the wound, e.g.in a highly exuding wound (These include cytokines, enzymes, growthfactors, cell matrix components, biological signalling molecules andother physiologically active components of the exudate.), and ormaterials contained in the irrigant that are potentially or actuallybeneficial in respect of wound healing, such as nutrients for woundcells to aid proliferation, and gases, such as oxygen, and such as thosenoted below in this regard, e.g. growth factors and otherphysiologically active materials. These may aid wound cell proliferationand new tissue growth that has a strong three-dimensional structureadhering well to and growing from the wound bed. This is a significantadvantage, in particular in chronic wounds. This is especially the casein those embodiments of the apparatus for aspirating, irrigating, and/orcleansing wounds where there is an inlet manifold as described below.This covers and contacts most of the wound bed with openings thatdeliver the fluid directly to the wound bed over an extended area.

It will be seen that the balance of fluid between fluid aspirated fromthe wound and irrigant supplied to the wound from the irrigant reservoirmay provide a predetermined steady state concentration equilibrium ofmaterials beneficial in promoting wound healing over the wound bed.Simultaneous aspiration of wound fluid and irrigation at a controlledflow rate aids in the attainment and maintenance of this equilibrium.

This confers an advantage over the wound dressings in use before thepresent invention with means for supplying physiologically active agentsunder conventional sequential aspiration and irrigation of the wound. Inthese, the physiologically active agents are often supplied to the woundbed through a foam, which acts as a baffle to reduce the rate ofdiffusion, thus creating a concentration gradient of the physiologicallyactive agents from a high concentration at the inlet point on thedressing to a low concentration at the wound bed. It is thereforedifficult to predict the concentration of actives at the wound bed. Thiseffect is exacerbated by a counter-flow of exudate from the wound bed.Many such dressings with means for supplying physiologically activeagents to the wound bed also have a concentration gradient of thephysiologically active agents across the wound bed from a highconcentration at the inlet point to a low concentration at the outletpoint. It is therefore difficult to supply a uniform concentration ofactives across the wound bed.

The inlet manifold in the wound dressings used in certain embodiments ofthe present invention covers and contacts most of the wound bed withopenings that deliver the fluid directly to the wound bed over anextended area, and therefore reduces the concentration gradient. It isthus easy to predict the concentration of actives at the wound bed, andthere tends to be no counter-flow of exudate from the wound bed. It isalso easy to supply a uniform concentration of actives across the woundbed.

Simultaneous aspiration and irrigation of the wound provides advantagesover topical bolus instillation, such as the pooled delivery of fluid tothe wound bed by the application of a conventional sequentialaspirate—irrigate—dwell cycle. These include (in addition to greaterbioavailability to all areas of the wound surface as above), prolongeddelivery between dressing changes and optimal dosing. In the lattercase, sequentially irrigating and aspirating a wound means the need toflood the wound with one or more static fluid physiologically activecomponent in higher dosage concentration than is necessary to achieve atherapeutically active level of such actives on the wound bed.

This is just to maintain a desired average therapeutically active levelof such actives on the wound bed during the dwell time period ofsequentially irrigating and aspirating a wound, since these dosageconcentrations levels tend to drop during this dwell time period in thecycle. It will be seen that normally the level of such actives iseffectively reduced to zero by the conventional sequential subsequentaspiration of the wound.

Less desirably, it has been observed that some of such physiologicallyactive components, for example factors such as TGFβ show differenteffects at high and low concentrations. An unnecessarily high dose toensure activity during the residence between typical bolus instillationsin conventional sequential irrigation—aspiration of the wound may resultin less than optimum dosing and performance of the body's own tissuehealing processes. Even less desirably, some of such physiologicallyactive components may have adverse effects at higher concentrations. Anunnecessarily high dose to ensure activity during the residence betweentypical bolus instillations in conventional sequential operation mayresult in undesirable effects on the wound bed. All of this may resultin slow healing and/or slowing down of the healing, and growth lacking astrong three-dimensional structure adhering well to and growing from thewound bed. This is a significant disadvantage, in particular in chronicwounds.

Some embodiments of the apparatus for aspirating, irrigating and/orcleansing wounds with supply to the wound bed under a positive pressuremay be advantageous. Application of a positive pressure to the woundunder the backing layer may make it possible to flood the tissueunderlying the wound with one or more physiologically active componentsin therapeutically active amounts. This may promote greater woundhealing than by treatment with static fluid physiologically activecomponent(s) alone or by sequential intermittent application of irrigantflow and aspiration

The prolonged delivery of such physiologically active components intherapeutically active amounts in a precise and time-controlled mannerby simultaneous aspiration and irrigation, together with (a) the removalof materials deleterious to wound healing from wound exudate, (b)without substantially diluting materials that are beneficial inpromoting wound healing in contact with the wound bed, and (c) thecontinuously supply of such materials to the wound, promotes greaterwound healing than (i) by treatment with the fluid physiologicallyactive component(s) alone, or (ii) by topical bolus instillation inknown aspirating and irrigating apparatus.

The supply of physiologically active materials may be effected at anyappropriate point for this purpose along the apparatus flow path. It isoften convenient to effect such supply to the wound via the fluidpassing through the wound dressing from irrigant in the fluid reservoirthat contains them.

Thus, one embodiment of the apparatus for irrigating, cleansing and/oraspirating wounds of the present invention is characterised in that itcomprises an irrigant fluid in the fluid reservoir which in turncomprises one or more physiologically active components in amounts topromote wound healing. The prolonged delivery of such physiologicallyactive components in therapeutically active amounts in a precise andtime-controlled manner by simultaneous aspiration and irrigation,together with (a) the removal of materials deleterious to wound healingfrom the wound, and (b) the continuous supply of materials that arebeneficial in promoting wound healing (that have been added using cellsor tissue) to the wound bed, promotes greater wound healing than (i) bytreatment with the fluid physiologically active component(s) alone, or(ii) by topical bolus delivery in known aspirating and irrigatingapparatus. Advantages over topical bolus delivery include greaterbioavailability to all areas of the wound surface, prolonged deliverybetween dressing changes and optimal dosing.

For example, factors such as TGFβ show different effects at high and lowconcentrations. Consequently, undesirable affects may be the result ofan unnecessarily high dose to ensure prolonged residence between topicalapplications.

Supply to the wound bed under a positive pressure may be advantageous,as appplication of a positive pressure to the wound under the backinglayer may make it possible to flood the tissue underlying the wound withone or more physiologically active components, added using cells ortissue, in therapeutically active amounts, to promote greater woundhealing, than by treatment with physiologically active component(s) instatic fluid alone.

It is foreseen that the actives to be added to the wound bed may be thenutrient medium, that human or mammalian cells e.g. keratinocytes,fibroblast or a mixture of these cells, or others for instance, havegrown in conditioned media. The cells will release beneficial actives tothe media e.g. TGFβ that would benefit the wound bed and aid healing ofthe wound.

In some embodiments of the present invention the actual cells themselveswith or without the cells growth media, may be used as an active to thewound bed to aid healing. In particular embodiments of the presentinvention different types of cells maybe used as actives at differenttimes of the healing process. For example, fibroblast type cells maybeused as an active to the wound bed to aid healing initially in order tohelp would remodelling and aid the wound to lay down structural fibres.Then keratinocytes or a larger proportion of keratinocytes thaninitially used before could be used as an active flowing along the woundbed to aid healing. Other cells could be used as well or combinationthereof.

It is foreseen that the cells (keratinocytes or fibroblasts) can aidhealing of the wound by giving beneficial healing components or bysticking to the wound bed and aiding healing directly.

When conditioned media is used, (the media that has had cells grown init) different conditioned media from different cell source may be usedand it is envisaged that having a particular order to which conditionedmedia to use may be important and aid healing. For example, conditionedmedia from fibroblast type cells or a mixture of cells comprising a highproportion of fibroblast cells may be used initially followed by aconditioned media from keratinocyte type cells or a mixture of cellscomprising a higher proportion of keratinocyte than used before. It isforeseen that this will aid healing of the wound.

Moving wound fluid aids in movement of biological signalling moleculesinvolved in wound healing (including such materials that have been addedusing cells or tissue) to locations in the wound bed that are favourableto (a) wound healing and/or to (b) cells that would otherwise not beexposed to them, e.g. in a highly exuding wound. This is especially thecase in those embodiments of the apparatus for aspirating, irrigatingand/or cleansing wounds where there is an inlet manifold that deliversthe fluid directly to the wound bed over an extended area. Suchmaterials include cytokines, enzymes, nutrients for wound cells to aidproliferation, oxygen, and other molecules that are beneficiallyinvolved in wound healing (including such materials that have been addedusing cells or tissue), such as growth factors, and others havingbeneficial effects (which may be further enhanced) in causingchemotaxis.

The apparatus for irrigating and/or aspirating wounds may be usedcyclically and/or with reversal of flow. The means for supplyingphysiologically active agents from cells or tissue often convenientlycomprises (a) an irrigant reservoir, (b) a container that contains acell or tissue component, and (c) at least one supply tube for supplyingphysiologically active agents from cells or tissue and/or irrigant tothe wound under the action of at least one device for moving fluidthrough the wound.

In use, irrigant is passed from the reservoir through the container thatcontains the cells or tissue and exits from it containing one or morephysiologically active component materials that are beneficial inpromoting wound healing that are expressed by the cells or tissue. Themodified irrigant (including such physiologically active agents as havebeen added from the cells or tissue) is moved by a device for movingfluid through the supply tube and dressing to the wound. Then inadmixture with wound exudate it is moved along the flow path, throughthe offtake tube.

In another embodiment of the apparatus for irrigating, cleansing and/oraspirating wounds of the present invention, the means for supplyingphysiologically active agents from cells or tissue to the woundcomprises (a) an irrigant reservoir, and (b) a container that contains acell or tissue component, (c) both connected in parallel to a supplytube for supplying physiologically active agents from cells or tissueand irrigant to the wound under the action of at least one device formoving fluid through the wound.

In this embodiment of the apparatus, the irrigant reservoir and thecontainer that contains a cell or tissue component may be, e.g.connected to the supply tube by a Y-junction. In use, irrigant is passedfrom the reservoir to the supply tube, and a fluid (which may be anutrient medium for the cells or tissue) containing one or morephysiologically active component materials that are beneficial inpromoting wound healing that are expressed by the cells or tissue ispassed from the container that contains the cells or tissue to thesupply tube. The irrigant in admixture with such physiologically activeagents as have been added from the cells or tissue is moved by a devicefor moving fluid through the wound to and through the wound.

In yet another embodiment of the apparatus for irrigating, cleansingand/or aspirating wounds of the present invention, the means forsupplying physiologically active agents from cells or tissue to thewound comprises (a) an irrigant reservoir, connected to (b) a firstsupply tube for supplying irrigant to the wound under the action of atleast one device for moving fluid through the wound, and (c) a containerthat contains a cell or tissue component, connected to (d) a secondsupply tube for supplying physiologically active agents from the cellsor tissue the wound dressing.

In use, irrigant is passed from the reservoir to the first supply tubefor supplying irrigant to the wound. The fluid containing one or morephysiologically active component materials that are beneficial inpromoting wound healing that are expressed by the cells or tissue ispassed from the container that contains the cells or tissue to thesecond supply tube for supplying physiologically active agents from thecells or tissue the wound dressing. Each is moved by a device for movingfluid through the wound to and through the wound. The irrigant isadmixed in the wound space with the physiologically active agents thathave been added from the cells or tissue.

In a further embodiment of the apparatus for irrigating, cleansingand/or aspirating wounds of the present invention, the means forsupplying physiologically active agents from cells or tissue to thewound comprises (a) an irrigant reservoir connected to (b) a containerthat contains a cell or tissue component, under the backing layer, andwhich communicates with the wound via at least one channel or conduitfor supplying physiologically active agents from cells or tissue andirrigant to the wound under the action of at least one device for movingfluid through the wound.

The container that contains a cell or tissue component may be integralwith the other components of the dressing, in particular the backinglayer. Alternatively, it may be permanently or demountably attached tothem/it, with an adhesive film, for example, or by heat-sealing. In use,irrigant is passed from the reservoir through the container thatcontains the cells or tissue and exits from it into the wound spaceunder the backing layer proximal face containing one or morephysiologically active component materials that are beneficial inpromoting wound healing that are expressed by the cells or tissue.

In yet a further embodiment of the apparatus for irrigating, cleansingand/or aspirating wounds of the present invention, the means forsupplying physiologically active agents from cells or tissue to thewound comprises (a) a first irrigant reservoir connected to (b) a supplytube for supplying irrigant to the wound under the action of at leastone device for moving fluid through the wound, and (c) a second irrigantreservoir connected to (d) a container that contains a cell or tissuecomponent, under the backing layer, and which communicates with thewound via at least one channel or conduit for supplying physiologicallyactive agents from cells or tissue and irrigant to the wound under theaction of at least one device for moving fluid through the wound. Thecontainer that contains a cell or tissue component may be integral withthe other components of the dressing, in particular the backing layer.Alternatively, it may be permanently or demountably attached to them/it,with an adhesive film, for example, or by heat-sealing.

In use, irrigant is passed from the first reservoir to the supply tubefor supplying irrigant to the wound. Irrigant is also passed from thesecond reservoir to the container. The fluid containing one or morephysiologically active component materials that are beneficial inpromoting wound healing that are expressed by the cells or tissue ispassed from the container that contains the cells or tissue to thesecond supply tube for supplying physiologically active agents from thecells or tissue the wound dressing. Each is moved by a device for movingfluid through the wound to and through the wound. The irrigant isadmixed in the wound space with the modified irrigant containingphysiologically active agents that have been added from the cells ortissue.

All of these embodiments of the means for supplying physiologicallyactive agents from cells or tissue to the wound may use cells or tissuesof two or more different types. In such systems, a first input cell ortissue type is often contained in a first container, and a second inputcell or tissue type is often contained in a second container. The twoinput cell or tissue types and containers may feed physiologicallyactive agents in parallel to the dressing and to the wound bed under theaction of at least one device for moving fluid through the wound.

To achieve therapeutically effective amounts of materials that arebeneficial in promoting wound healing, a fluid flow though and/or overthe cells or tissue may have to be maintained over multiple cycles, withsignificant dwell times and/or over significant periods of time.

Thus, in those embodiments of the means for supplying physiologicallyactive agents from cells or tissue to the wound described above, thecontainer that contains a cell or tissue component may be provided with(a) means for recycling nutrient medium for the cells or tissue from andback to a nutrient medium reservoir, e.g. a loop comprising thereservoir, connected to the container that contains the cells or tissue,with a pump, and in particular (b) means for switching fluid flowbetween recycling around the loop comprising the reservoir and thecontainer and supply to the relevant supply tube. Such means forswitching fluid flow may comprise at least one one-way valve in the loopand in the fluid supply tube, or a two way valve connecting the supplytube and the loop.

In use, nutrient medium for the cells or tissue is recycled from andback to a nutrient medium reservoir in the loop comprising the reservoirand the container that contains the cells or tissue, with a pump, overmultiple cycles, with significant dwell times and/or over significantperiods of time until the cell proliferation in the cells or tissue inthe container that contains the cells or tissue and/or the expression bysuch cells or tissue of one or more physiologically active componentmaterials that are beneficial in promoting wound healing have achievedthe desired levels.

Recycling nutrient medium for the cells or tissue from and back to thenutrient medium reservoir is then stopped, and supply to the relevantsupply tube is started.

This may be achieved by stopping the pump and/or closing a one-way valvein the loop and opening on in the supply tube, or by switching a two wayvalve connecting the supply tube and the loop. The necessary desiredlevels of physiologically active component materials, valves, pumps,number of cycles, dwell times and/or time periods will be apparent tothe skilled person.

As noted above, in another embodiment of the apparatus for aspirating,irrigating and/or cleansing wounds, a particular advantage is that themeans for supplying physiologically active agents from cells or tissueto the wound lies within the wound dressing. In use, irrigant is passedfrom the reservoir through the cells or tissue component for supplyingphysiologically active agents to the wound which lies within the wounddressing, and exits from it containing one or more componentphysiologically active component materials that are beneficial inpromoting wound healing that are expressed by the cells or tissue. Themodified irrigant (including such physiologically active agents as havebeen added from the cells or tissue) in admixture with wound exudate ismoved by the device for moving fluid through the offtake tube along theflow path.

Thus, one embodiment of the apparatus for irrigating, cleansing and/oraspirating wounds of the present invention is characterised in that itthe means for supplying physiologically active agents from cells ortissue to the wound comprises (a) an irrigant reservoir fluidicallyconnected to (b) a wound dressing that contains a cell or tissuecomponent.

The wound dressing backing layer, which is capable of forming arelatively fluid-tight seal or closure over a wound, and the wound beddefine a wound space, which contains cells or tissue. As noted above fora separate container, the wound space may contain a cell or tissuecomponent that is not bound to an insoluble and immobilised substrateover and/or through which the irrigant and/or wound exudate from thewound passes. It then also appropriately comprises two or more integerswhich are permeable to the wound exudate or a mixture with irrigant, buthave apertures, holes, openings, orifices, slits or pores ofsufficiently small cross-dimension to hold the cell or tissue component,and to retain particulates, e.g. cell debris, in the hollow body.

Each of the integers may then effectively form a macroscopic and/ormicroscopic filter. Alternatively, it may contain a cell or tissuecomponent that is bound to an insoluble and immobilised substrate overand/or through which the irrigant and/or wound exudate from the woundpasses, e.g. a scaffold. This will often be of a material, and maytypically be in the form, noted above as amongst those that are suitablefor such components of a separate container that contains a cell ortissue component.

The wound space may contain a cell or tissue component at anyappropriate point in contact with the irrigant and/or wound exudate, andthe component may be as appropriate, adhered or otherwise secured to anyinteger of the wound dressing, e.g. the dressing backing layer or awound filler, or it may be a separate structures, permanentlyunattached. It may often lie in contact with the wound bed. Where itdoes so, it may be advantageous if it is (a) bound to an insoluble andimmobilised substrate over and/or through which the irrigant and/orwound exudate from the wound passes, or (b) not bound to an insolubleand immobilised substrate, but comprised in two or more integers whichare permeable to the wound exudate or a mixture with irrigant, and (c)comprises a biodegradable mesh, grid, lattice, net or web, withapertures, holes, openings, orifices, slits or pores of smallcross-dimension in contact with the wound bed.

The cell or tissue component in contact with continuously suppliedirrigant and/or wound exudate has the ability to add elements beneficialto wound healing to the irrigant, but the same elements also aidproliferation of wound bed cells into the apertures, holes, openings,orifices, slits or pores of small cross-dimension of the biodegradablemesh, grid, lattice, net or web, which is also beneficial to woundhealing.

In general, the tissue component has the ability to elaborate or expressmaterials beneficial to wound healing to the irrigant to modify theirrigant. As described in further detail hereinafter, such elementsbeneficial to wound healing may be biochemical, e.g. enzymatic orphysical antagonists to elements detrimental to wound healing in theexudate and/or exudate and irrigant.

An additional embodiment of the apparatus for irrigating, cleansingand/or aspirating wounds of the present invention is characterised inthat the physiologically active components that have been added usingcells or tissue in amounts to promote wound healing comprise materialsthat are beneficial in promoting wound healing by removing materials orby regulating, limiting or inhibiting processes deleterious to woundhealing.

Depending on the particular type of wound being treated and theparticular cells or tissue used in the present apparatus for aspirating,irrigating and/or cleansing wounds, the deleterious materials to beremoved may include (a) proteases, such as serine proteases, e.g.elastase and thrombin; cysteine proteases; matrix metalloproteases, e.g.collagenase; and carboxyl (acid) proteases; (b) inhibitors ofangiogenesis such as thrombospondin-1 (TSP-1), Plasminogen activatorinhibitor, or angiostatin (plasminogen fragment); (c) pro-inflammatorycytokines such as tumour necrosis factor alpha (TNFα) and interleukin 1beta (IL-1β); and (d) inflammatories, such as lipopolysaccharides, ande.g. histamine.

Materials deleterious to wound healing that are removed using theapparatus may also include: (a) oxidants, such as free radicals, e.g.peroxide and superoxide; (b) iron II and iron III; (c) all involved inoxidative stress on the wound bed; (d) proteases, such as serineproteases, e.g. elastase and thrombin; cysteine proteases; matrixmetalloproteases, e.g. collagenase; and carboxyl (acid) proteases; (e)endotoxins, such as lipopolysaccharides; (f) autoinducer signallingmolecules, such as homoserine lactone derivatives, e.g. oxo-alkylderivatives; (g) inhibitors of angiogenesis such as thrombospondin-1(TSP-1), plasminogen activator inhibitor, or angiostatin (plasminogenfragment); (h) pro-inflammatory cytokines such as tumour necrosis factoralpha (TNFα) and interleukin 1 beta (IL-1β), (i) oxidants, such as freeradicals, e.g., e.g. peroxide and superoxide; and (j) metal ions, e.g.iron II and iron III, all involved in oxidative stress on the wound bed.

It is believed that aspirating wound fluid aids in removal from of thematerials deleterious to wound healing from wound exudate and/orirrigant, whilst distributing materials that are beneficial in promotingwound healing in contact with the wound. A steady state concentrationequilibrium of materials beneficial in promoting wound healing may beset up between in the irrigant and/or wound exudate. Aspirating woundfluid aids in the quicker attainment of this equilibrium

Materials beneficial to wound healing that are distributed include (a)cytokines, enzymes, growth factors, cell matrix components, biologicalsignalling molecules and other physiologically active components of theexudate and/or (b) materials in the irrigant that are potentially oractually beneficial in respect of wound healing, such as nutrients forwound cells to aid proliferation, gases, such as oxygen.

Again, depending on the particular type of wound being treated and theparticular cells or tissue used in the present apparatus for aspirating,irrigating and/or cleansing wounds, the beneficial materials to be addedmay include antagonists to the materials deleterious to wound healing inthe wound exudate, such as, for example (a) enzymes or others, such asprotease inhibitors, such as serine protease inhibitors, cysteineprotease inhibitors; matrix metalloprotease inhibitors; and carboxyl(acid) protease inhibitors; (b) binders and/or degraders, such asanti-inflammatory materials to bind or destroy lipopolysaccharides, e.g.peptidomimetics. They further include (a) peptides (including cytokines,e.g. bacterial cytokines, such as α-amino-γ-butyrolactone andL-homocarnosine); and (b) other physiologically active components.

Examples of antagonists to such materials also include (a) naturalproteins or recombinant-produced protein, proteinase inhibitors, such astissue inhibitors of metalloproteinases (TIMP 1 to 4) and alpha1-antitrypsin (AAT), aprotinin, α-2-macroglogulin; (b) antibodies orother molecules at inappropriate levels that inhibit or inactivateprocesses or materials deleterious to wound healing, such as matrixmetalloproteinases (MMPs), neutrophil elastase, inhibitors of new bloodvessel formation (angiogenesis) such as thrombospondin or kallistatinand combinations thereof.

The irrigant may alternatively or additionally, where appropriate,deliver a steady supply of natural proteins or recombinant-producedprotein debriding agents to remove and limit eschar, necrotic cells andtissues from the wound bed. Examples of such include stretoptokinase,plasmin, trypsin, collagenases, and other selective proteases orfibrinolytic factors and combinations thereof.

The irrigant supplied to the wound dressing may alternatively oradditionally, where appropriate, contain materials added using cells ortissue such as (a) antioxidants, such as ascorbic acid or stablederivatives thereof and (b) free radical scavengers, such as gutathioneor natural proteins or recombinant-produced proteins such as superoxidedismutase (SOD), or (c) free radical generators to balance the oxidativestress and oxidant potential of the wound bed in order to maximize theopportunity for wound healing.

The active material may act beneficially on the wound bed and have theability to aid wound healing, as it is passed by the device through theflow path, through biochemical, enzymatic or physical means without anysuch role as a biochemical, enzymatic or physical antagonist. Examplesof such components (however supplied) include: (a) autologous,allogeneic or xenogeneic blood or blood products, such as plateletlysates, plasma or serum; (b) natural purified proteins orrecombinant-produced protein growth factors, such as platelet derivedgrowth factor (PDGF), vascular endothelial growth factor (VEGF),transforming growth factor alpha (TGFα) or transforming growth factorbeta (TGFβ-1, 2 or 3), basic-fibroblast growth factor (b-FGF also knownas FGF2), epidermal growth factor (EGF), granulocyte-macrophagecolony-stimulating factor (GM-CSF); insulin like growth factor-1 (IGF-1)and keratinocyte growth factor 2 KGF2 (also known as FGF7); (c) naturalpurified proteins or recombinant produced protein cytokines such as theinterleukin β (IL1β), or interleukin 8 (IL-8) and (d) otherphysiologically active agents whether present normally in acute orchronic wounds, that can be augmented in the irrigant fluid to be ofbenefit to the wound bed, when such therapy is applied, and combinationsthereof.

An additional embodiment of the apparatus for irrigating, cleansingand/or aspirating wounds of the present invention is characterised inthe physiologically active components in amounts to promote woundhealing comprise materials that are beneficial in promoting woundhealing by removing materials or by regulating, limiting or inhibitingprocesses deleterious to wound healing from wound exudate.

Examples of such materials include (a) natural purified proteins orrecombinant-produced protein, proteinase inhibitors, such as tissueinhibitors of metalloproteinases (TIMP 1 to 4) and alpha 1-antitrypsin(AAT), aprotinin, α-2-macroglogulin; (b) antibodies or chemicallysynthesised molecules at inappropriate levels that inhibit or inactivateprocesses or materials deleterious to wound healing from wound exudate,such as matrix metalloproteinases (MMPs), neutrophil elastase,inhibitors of new blood vessel formation (angiogenesis) such asthrombospondin or kallistatin and combinations thereof.

The irrigant may alternatively or additionally, where appropriate,deliver a steady supply of natural purified proteins orrecombinant-produced protein debriding agents to remove and limiteschar, necrotic cells and tissues from the wound bed. Examples of suchinclude stretoptokinase, plasmin, trypsin, collagenases, and otherselective proteases or fibrinolytic factors and combinations thereof.

The irrigant supplied to the wound dressing, optionally under a positivepressure on the wound bed, may alternatively or additionally, whereappropriate, contain (a) antioxidants, such as ascorbic acid or stablederivatives thereof and (b) free radical scavengers, such as gutathioneor natural purified proteins or recombinant-produced proteins such assuperoxide dismutase (SOD) or (c) free radical generators (such ashydrogen peroxide) to balance the oxidative stress and oxidant potentialof the wound bed in order to maximize the opportunity for wound healing.

The irrigant supplied to the wound dressing under a negative or positivepressure on the wound bed may alternatively or additionally, whereappropriate, contain nutrients for wound cells to aid proliferation ormigration or the synthesis of matrix components or factors beneficial towound healing, such as sugars, amino acids, purines, pyrimidines,vitamins, metal ions or minerals, or any such ingredients that may befound in either serum containing or serum-free cell culture medium ormight be used as nutritional supplements.

The irrigant supplied to the wound dressing under a negative or positivepressure on the wound bed may alternatively or additionally, whereappropriate, contain medicaments, such as antimicrobials, examples ofwhich include antibacterial agents, for example triclosan, iodine,metronidazole, cetrimide, chlorhexidine acetate; antifungal agents, forexample sodium undecylenate, chlorhexidine, iodine or clotrimoxazole;antibiotics such as ciprofloxacin or clindamycin.

The irrigant supplied to the wound dressing under a negative or positivepressure on the wound bed may alternatively or additionally, whereappropriate, include local analgesics/anaesthetics, such as lignocaine,bupivicaine, or diclofenac to reduce wound pain or pain associated withthe dressing:

The irrigant supplied to the wound dressing under a negative or positivepressure on the wound bed may alternatively or additionally, whereappropriate supply materials to achieve the delivery of nucleic acidmolecules as active genes or gene-containing vectors (DNA, RNA ormodified versions thereof), as naked molecules, molecules complexed withnucleic acid binding carriers, molecules within liposomes or as virusvectors to give steady, measured delivery of gene therapeutic moleculesto wound bed cells.

In the means for supplying physiologically active agents from cells ortissue to the wound, the irrigant from the reservoir that passes intoand through the cell or tissue component often conveniently comprisescell culture medium species. Examples of the latter include (a) traceelements and/or other nutrients such as amino acids, sugars, lowmolecular weight tissue building blocks, purines, pyrimidines, vitamins,metal ions or minerals, and/or (b) gases, such as air, nitrogen, oxygenand/or nitric oxide, (c) to aid proliferation of the cells or tissue inthe means and/or steady, measured expression and supply ofphysiologically active agents. In such case, materials that are listedabove are also suitable therapeutic molecules to supply to wound bedcells to aid proliferation of the cells or tissue, and/or which areotherwise beneficial to wound healing. In such case, it may be desirableto provide a system in which the irrigant from the reservoir that passesinto and through the cell or tissue component comprises cell culturemedium species and thereafter is supplied to the wound bed via a supplytube into the flowpath wherever appropriate, so that such cell culturemedium species pass with the irrigant to the wound bed.

The irrigant from the reservoir may be used to maintain an optimumtemperature of the cells or tissue and/or for regulating the exchange ofgases in a conventional manner apparent to the skilled person. It isnecessary for such a system to also irrigate the wound at a practicalrate with the physiologically active components in therapeuticallyactive amounts.

Automated, programmable systems which can regulate the wound irrigantparameters and functions listed above in a precise and time-controlledmanner are amongst those that are particularly suitable for use.

The tissue component may be an ex vivo (autologous, allogeneic orxenogenic) uncultured tissue explant. Alternatively the tissue componentmay be formed from separated or partially separated cells which haveeither been used without a period of culture or they may have beencultured in vitro. The process of culture may involve growth andproliferation or just incubation in culture. The source tissues may betissue from any organ such as skin, muscle, bone, neural, connectivetissue, intestinal, liver or amniotic tissue and other organs orcombinations thereof, whose cells and tissue retain the appropriateproperties. The cells or tissue may be fully viable or viable, butrendered non-dividing through irradiation or chemical treatment, orrendered non-viable after an appropriate period of culture.

Alternatively, the cells or tissue may be genetically modified toincrease production of a particular material, e.g. a protein that isbeneficial in promoting wound healing, such as a growth factor, anextracellular matrix component or fragments thereof, and otherphysiologically active components, or a biochemical, e.g. enzymatic orphysical antagonists to elements detrimental to wound healing in theexudate and/or exudate and irrigant.

The tissue component that provides the active material that actsbeneficially on the wound bed may consist of a co-culture. A co-cultureencompasses the in vitro or ex vivo culture of two or more cell types ortissue explants. This might be with one or both input cells or tissuesfully viable or viable, but rendered non-dividing, through irradiationor chemical treatment, or rendered non-viable after an appropriateperiod of culture. Alternatively, the cells or tissue may be geneticallymodified to increase production of a particular material, e.g. a proteinthat is beneficial in promoting wound healing, such as a growth factor,an extracellular matrix component or fragments thereof, and otherphysiologically active components, or a biochemical, e.g. enzymatic orphysical antagonists to elements detrimental to wound healing in theexudate and/or irrigant.

The input cells or tissues may be intimately mixed or intermingled, orthey may be present as layers one on the other. In some systems a semipermeable membrane or matrix between the component cells or tissuesallows communication through biochemicals or proteins or other signals,but no cell apposition between the input cell types. In further systemsmodified irrigant is collected from one input cell or tissue type andgiven to the second input cell or type and given back to the first inputcell type (sequentially or continuously) to generate the optimal output.

The cell or tissue component may be activated either singly orrepeatedly through the delivery of biochemical, protein, enzymatic orphysical means or through electromagnetic irradiation, ultrasonic orelectrical stimulation. Preferably the present apparatus for aspirating,irrigating and/or cleansing wounds is a conventionally automated,programmable system which can cleanse the wound with minimalsupervision.

Scaffold

In certain embodiments, the apparatus for aspirating, irrigating, and/orcleansing wounds further comprises a biodegradable scaffold.

A significant advantage, in particular in chronic wounds, is that in usegranulation tissue is encouraged to grow onto and/or into a scaffoldthat lies between the wound dressing and the wound bed. The effect maybe further enhanced by the circulation over the wound bed of irrigantfrom the fluid reservoir which contains nutrients for wound cells to aidproliferation, and other molecules that are beneficially involved inwound healing and/or that are favourable to the wound healing process.

A particular advantage is that it is unnecessary to remove thisgranulation tissue in-growth on dressing change, as the scaffold is leftbetween the wound film dressing and the wound bed to biodegrade. Thisminimizes trauma and any need for debridement. A more specific advantageis that the scaffold prevents the overgrowth of tissue in the woundarea. Another advantage of this apparatus is its use with pressuresores: the device can be placed in the depths of the wound and thepatient can lie upon it without either affecting the utility of thedevice or further damaging the wound. This becomes critical if thepatient cannot be moved from this posture for medical reasons.

In use, the scaffold is placed over substantially the expanse of thewound, and its size and configuration can be adjusted to fit theindividual wound. It can be formed from a variety of apertured,semi-rigid materials. By ‘apertured’ herein is meant materials that areporous, apertured, holed, open-mesh, slit, incised and/or cut and thelike. The material should be sufficiently apertured to allow forinvasion by all manner of cells involved in the process of tissue repairand wound healing, and/or for the inward growth of blood vessels, andsufficiently rigid to prevent wound overgrowth and collapse undersuction.

Suitable biomaterials for the biodegradable scaffold includepoli(hydroxyl acids) and esters thereof, such as poly(glycolic acid),poly(L-lactic acid), poly(D-lactic acid) and esters thereof, andcopolymers and blends of the aforementioned. Additionally, biologicallysourced biodegradable polymeric materials such as substantially proteinbased polymers, for example; collagens, fibronectins, or fibrins, eitheras whole molecules or those subjected to proteolytic or chemicaltreatments, in either degraded or native conformations, or modifiedproteins produced by nucleic acids recombinant techniques, orcombination thereof. Further acceptable scaffolds will be combinationsof protein-based scaffolds and carbohydrate based polymers such asglycosoaminoglycans, chitosans, cellulose or alginate molecules.Suitable materials also include human or animal derived tissuesprocessed in means to make them acceptable in placement into the woundsuch as skin, alimentary tract or connective tissues. The scaffold maybe formed in a variety of apertured, semi-rigid forms.

These forms may be essentially two-dimensional, such as sheets, layers,films, flexible panels, meshes, nets, webs or lattices. They may beplaced in the wound as dry, hydrated or gel based formulations. Oneembodiment of apertured or holed scaffold comprises a section ofhoneycombed polymer sheet cut to the shape of the wound.

Where the scaffold is in an essentially two-dimensional apertured,semi-rigid form, such as a sheet, layer, film, flexible panel, mesh,net, web or lattice, it may be designed in a configuration that is ableto conform well to the wound bed on insertion into the wound. Thisconforming to shape is then a particular advantage in those embodimentswhere the wound dressing is used on deeper wounds, especially where awound filler is used to urge the wound dressing towards the scaffold andwound bed, as described hereinafter in connection with the wounddressing.

By way of example, such a scaffold may be in the form of a deeplyindented circular disc much like a multiple Maltese cross or a stylisedrose, as is described hereinafter in connection with an inlet manifoldshown in FIG. 18b . This form is able to conform well to the wound bedon insertion into the wound, especially a deeper wound, by the armsclosing in and possibly overlapping. The form of the scaffold may alsobe three-dimensional, such as sheets, layers, films, flexible panels,meshes, nets, webs and lattices, folded, creased, pleated, tucked,crinkled, crumpled, screwed up or twisted into a three-dimensional form.Alternatively, these forms may be inherently three-dimensional, such asmultilayers of films, flexible panels, meshes, nets, webs and lattices,or three-dimensional meshes, nets, webs and lattices, and favourablyfoams. They may be placed in the wound as dry, hydrated or gel basedformulations.

One embodiment of an apertured or holed scaffold comprises a section ofbiodegradable polymer mesh, which permits (a) fluid supply towards thewound bed, (2) the withdrawal of tissue fluid through the pores of thescaffold and (3) the ingrowth of cells to yield the eventual replacementof the scaffold with new tissue under the influence of the suctionforce. A favoured embodiment of this apparatus comprises a section ofknitted two- or three-dimensional mesh, in particular three-dimensionalmesh. A preferred embodiment of this apparatus comprises a section ofthree-dimensional sponge as the biodegradable scaffold. Such scaffoldcan vary in thickness and rigidity, although it is preferred that a softmaterial be used for the patient's comfort if the patient must lie uponthe device during its operation. Where the biodegradable scaffoldcomprises a mesh, the latter may be unwoven, woven or knitted,preferably knitted, and preferably three-dimensional.

Flow Stress

In some embodiments, the apparatus may include means for providing flowstress. The motion of fluids across a surface results in shear stresseswithin the surface. On a micropscopic level such flow may cause otherlocalised or general forces on areas of the surface. These forces orstresses are encompassed in the term flow stress as used herein. Theseare effects such as, but not limited to an increase in cellproliferation, debridement of necrotic tissue, removal of slough and toallow alignment of collagen fibres. This leads to improved breakingstrength of tissue growth, to a strong three-dimensional structureadhering well to and growing from the wound bed, and reduction of woundrecurrence.

The terms stress and strain have slightly different meanings, but in thecontext of this application, are often used interchangeably. “Stress”refers to a physical force acting upon a surface or structure, in thiscase a wound bed. Stress is typically defined as force per unit area ona surface. “Strain” refers to a mechanical deflection of a surface orstructure caused by stress, again in this case a wound bed. Stress maycause strain, or vice versa, but in the context of the presentapplication, where the term stress is used, it should be understood torefer to stress or strain of the wound bed. For example, applying apositive pressure to a wound bed will apply a stress to the surface ofthe wound bed, but will also apply a strain as the wound bed is aresilient structure which will deflect as a result of the pressure. Onthe other hand deflection of the wound bed in one area (i.e. applying astrain) may cause stress and/or strain in another area. Accordinglywhere the term stress or strain is used in the present application, theyshould not be taken in their strict mechanical meaning (although thatmay be appropriate) but should be understood to mean the deflection orapplication of force to the cells of the wound bed and or surroundingareas.

Such a stress or strain across the wound bed and optionally tissuesurrounding the wound, e.g. an optionally varying positive and/ornegative pressure applied to the wound, has been found to result in anincrease in improvements to wound healing, such as an increase in cellproliferation, revascularisation, improved breaking strength andreduction of wound recurrence.

The resultant tissue growth has a strong three-dimensional structureadhering well to and growing from the wound bed. It also stimulatesblood flow in underlying tissue and optionally tissue surrounding thewound.

Removal of fluid by optionally varying negative pressure leads toreduction of interstitial oedema and pressure directly affecting thelymphatic and capillary system, restoring lymph function.

All of these are beneficial to wound healing.

The application of stress and/or strain to a wound bed to improvehealing is equally applicable to both sequential systems (i.e.empty/fill cycles) or simultaneous irrigate/aspirate systems. Althoughit is generally preferred to use a simultaneous system due to thebenefits of such a system, there may be circumstances where a sequentialsystem is preferred, e.g. due to cost.

Removal of excess fluid assists with the reduction of interstitialoedema and pressure directly affecting the lymphatic and capillarysystem, restoring lymph function and stimulating blood flow.

The means for applying flow stress to the wound bed in the apparatus foraspirating, irrigating and/or cleansing a wound according to anembodiment of the present invention include means for applying,controlling and/or varying fluid (i.e. irrigant and/or wound exudate)flow under the wound dressing as hereinbefore defined at any appropriatepoints across the wound bed.

These include (a) features in the conformation of the wound dressing, inparticular in the wound facing face of the dressing in relation to thewound bed in use, and/or (b) features in the rest of the system in whichthe fluid moves, in particular the throughput of the device for movingfluid through the wound which give the appropriate or desired fluid flowrate or velocity of the irrigant and/or wound exudate under the wounddressing to cause flow stress at any appropriate points across the woundbed. These are described in detail hereinafter in connection with theoperation of the apparatus.

It is sufficient to note here that features in the conformation of thewound dressing, in particular in the wound facing face of the dressingin relation to the wound bed in use, which give the appropriate ordesired fluid flow rate or velocity of the irrigant and/or wound exudateunder the wound dressing to cause flow stress at any appropriate pointsacross the wound bed include irrigant inlet manifolds which contact orlie very close to the wound bed, irrigant inlet or outlet manifoldscomprised in the dressing, which have apertures or pores by the woundbed that are of suitable total area over an extended area, projections,such as bulges or protuberances on the wound-facing face of thedressing, that are capable of directing flow.

Features in the rest of the system in which the fluid moves, inparticular the throughput of the device for moving fluid through thewound, which give the appropriate or desired fluid flow rate or velocityof the fluid (i.e.irrigant and/or wound exudate) under the wounddressing to cause flow stress at any appropriate points across the woundbed include devices which impose: (i) relatively high flow rates orvelocities, or rates of change in the flow rates or velocities, ofirrigant and/or wound exudate flow under the wound dressing at anyappropriate points across the wound bed; and/or (ii) a relatively highpressure drop between the interior of an inlet manifolds comprised inthe dressing and the wound bed.

Change in the flow velocities of fluid (i.e. irrigant and/or woundexudate) flow under the wound dressing at any appropriate points acrossthe wound bed include changes from positive to negative over the woundbed, i.e. reversing flow, in particular with relatively high rates offlow across the wound bed.

As noted hereinbefore, certain embodiments of the present inventionadvantageously provides a means for combining more than one therapy in asingle dressing system, such as (a) removal of materials deleterious towound healing from wound exudate, and (b) promoting wound healing, bystimulating new tissue growth adhering well to and growing from thewound bed, by creating stress across the wound bed and optionally tissuesurrounding the wound.

Such flow stress across the wound bed may also advantageously actagainst wound bacteria, by (a) breaking up biofilm growth before itdevelops a strong three-dimensional structure adhering well to andgrowing from the wound bed and/or (b) releasing them to be attacked bythe body in the wound. It may aid in the debridement of slough, escharand necrotic tissue growth from the wound, and in preventing adhesion ofwound tissue to the dressing.

Examples of suitable ways in which flow stress can be achieved includeapplying (a) an optionally varying and/or reversing linear flow and/or(b) a relatively high rate of irrigant flow across the area of the woundbed. That is, flow stress across the wound may be provided by means of(a) a linear flow of irrigant across the wound bed, (b) a relativelyhigh rate of irrigant flow across the wound bed, or (c) a combination ofthe two.

Generally simultaneous irrigate/aspirate systems lead themselves toincluding flow stress as fluid can be induced to flow between an inletand outlet as required (this is described in more detail below).However, sequential systems are also suitable for inducing flowstresses. In particular these stresses may be induced during the fillingand emptying cycles.

When used herein, the term ‘linear’ refers to flow that is locallylinear on a cellular scale, and thus includes not only parallel flow,but also radial streaming, and spiral, helical, spirohelical andcircular streaming. Preferred linear flows include radial streaming fromthe center out and from the periphery in to center, in particular fromthe periphery in to the center as this may increase the cell motilityvelocity of keratinocytes towards the center, and so promotere-epithelialisation. It is also preferred that the flow rate isrelatively uniform across the wound to achieve a uniform stimulationapplied across the wound bed.

The velocity of the fluid thereover may be constant, but it may bevaried, preferably cyclically, either randomly or regularly. Usually thedirection of the wound irrigant and/or wound exudate is held constant,but the flow rate may be varied positively and negatively, preferablycyclically, and either randomly or regularly.

Cyclical application of flow stress across the wound bed may result in afurther increase in cell proliferation and in the breaking strength oftissue growth, and in a strong three-dimensional structure of tissueadhering well to and growing from the wound bed.

The stimulation of the healing of wounds may also be effected byregularly or randomly pulsing a flow velocity applied to the wound atany appropriate point for this purpose. The frequencies of such pulsedflow stressing across the wound will be (a) substantially higher thanthose of the cycles of flow velocity to the wound bed for thestimulation of the healing of wounds referred to above, but (b) less(generally substantially less) than the frequencies of ultrasound thatmay be used on the wound bed in alternative methods of therapy. Pulsingthe flow over the wound may advantageously also provide a means toover-ride pain, similar to TENS.

Stimulus to the wound bed by applying an optionally varying flowvelocity (i.e. cyclical) and agitation of the wound bed to stimulate thecells by regularly or randomly pulsing any flow applied to the wound aremutually compatible. They may, as appropriate, be applied alone ortogether. Flow may be applied continually or in periodic episodesbetween which the apparatus is operating in lower flow regimes, orindeed where the apparatus is working on a sequential (fill/empty)basis.

Thus, an embodiment of the apparatus for irrigating, flow stressingand/or cleansing wounds is characterised in that it comprises means forsupplying optionally varying linear flow velocity, which is optionallypulsed, to a wound bed for the stimulation of the healing of the wound.Examples of suitable linear velocities are up to 0.03 m/s in a 100micrometre gap or channel between wound bed and dressing creating ashear stress on the wound bed of the order of 12-13 dynes/cm². Inpractice, such a velocity will be of the order of 0.06 to 6, e.g. 0.2 to2, for example 0.6 mm/s in a 100 micrometer channel between wound bedand dressing creating a shear stress on the wound bed of the order of0.06 to 20, e.g. 0.6 to 6, for example 0.6-2 dynes/cm², for a typicalwound exudate and/or isotonic saline irrigant. By way of example, afluid velocity of e.g. 0.3 m/s will typically be a flow rate of 70-200ml/hr for a 100 mm diameter wound.

It will be appreciated that the shear stress (and consequentially flowstress) on the wound bed will increase with the viscosity of the fluidpassing across it. This property may be used to increase or decrease theflow stress generated by a given flow velocity.

Another embodiment of the apparatus for irrigating, flow stressingand/or cleansing wounds is characterised in that it comprises means forsupplying optionally varying relatively high flow velocity, which isoptionally pulsed, to a wound bed for the stimulation of the healing ofthe wound.

As noted hereinbefore, in certain embodiments of the present invention,the flow velocity of the fluid may be constant, but may be varied,preferably cyclically, either randomly or regularly. In bothembodiments:

Examples of suitable frequencies of such regular cycles of flowvelocities for the stimulation of the healing of wounds include 1 to 48per 24 hr.

Examples of preferred frequencies of such regular cycles of flowvelocities for the stimulation of the healing of wounds include 12 to 24per 24 hr, e.g. 2 to 1 per hr.

Examples of suitable waveforms of such cycles either regularly orrandomly for the stimulation of the healing of wounds include curved,e.g. sinusoidal, and sawtooth for higher frequencies, and usually squarefor lower frequencies.

Examples of means for applying flow stress to the wound bed includesupplying irrigant to, and letting out irrigant and/or wound exudatefrom, the wound dressing in regular or random cycles and/or pulsedeither regularly or randomly.

Examples of suitable frequencies of such regular pulses for thestimulation of the healing of wounds include 1 to 60 per min, e.g. 5 to10 per min.

Examples of preferred frequencies of such regular pulses for thestimulation of the healing of wounds include 30 to 60 per min, e.g. 10to 20 per min.

Examples of suitable waveforms of such pulses either regularly orrandomly for the stimulation of the healing of wounds include curved,e.g. sinusoidal, sawtooth, square and a systolic-diastolic asymmetricsawtooth.

Examples of means for applying an optionally varying linear flowvelocity at any appropriate point for flow stressing the wound include awound dressing as hereinbefore described defined that comprises one ormore modules capable of imposing linear flow on the irrigant at anyappropriate point across the wound bed.

Thus, one favoured embodiment of the apparatus for irrigating, stressingand/or cleansing wounds is characterised in that it comprises a wounddressing as hereinbefore defined that comprises one or more modulescapable of imposing linear flow on the irrigant across the wound bed atany appropriate point for flow stressing the wound.

Examples of suitable modules capable of imposing linear flow on theirrigant across the wound bed at any appropriate point for stressing thewound include the following in conjunction with a wound-facing face ofthe dressing that is in contact with or very close to the wound bed.

A plurality of inlet and/or outlet pipes maybe disposed in an arrayunder the wound-facing face of the dressing, so as to allow passage ofirrigant and/or wound exudate through the wound to take place in acontrollable linear stream.

Irrigant inlet and/or outlet manifolds with respectively a plurality ofinlet and/or outlet apertures, and connected in turn to at least oneirrigant inlet pipe(s) and/or outlet pipe(s) may be provided under thewound-facing face of the wound dressing. (Fluid passes between thesestructures and they assist in channelling flow of irrigant and/or woundexudate through the wound in a controllable stream.) These may, forexample, include tubules in an array connecting into a manifold.

Projections, such as bulges or protruberances, may be provided on thewound-facing face of the dressing. Alternatively or additionally, whereappropriate depressions may be provided on the wound-facing face of thedressing. Both will often run within the wound between the inlet pipe(s)and the outlet pipe(s) (or manifolds) under the wound-facing face of thewound dressing. Fluid-inflatable bodies that lie in the wound in use andform projections are described hereinafter in greater detail. Ofparticular interest are fluid-inflatable irrigant inlet manifoldscomprised in the dressing, which are inflated by admitting irrigantfluid. Examples of preferred such modules include fluid-inflatableirrigant inlet manifolds comprised in the dressing as describedhereinafter in greater detail. The modules and backing layer may becompletely separate integers, separate integers which are attached, forexample by heat sealing, to each other, or they may be integral, i.e.may be formed of a single piece of material. In all cases the modulesmay be disposed to impose linear flow between the inlet pipe(s) (ormanifold) and the outlet pipe(s) (or manifold) under the wound-facingface of the wound dressing, as hereinbefore describe, in a number ofdifferent modes.

Examples of forms of linear flow imposed on the irrigant across thewound bed at any appropriate point for stressing the wound include notonly parallel flow, but also radial streaming, and spiral, helical,spirohelical and circular streaming. Preferred linear flows includeradial streaming. Preferred linear flows include radial streaming fromthe center out and from the periphery in to center, in particular fromthe periphery in to the center as this may increase the cell motilityvelocity of keratinocytes towards the center, and so promotere-epithelialisation.

Thus, the modules may comprise a plurality of inlet and/or outlet pipes(or manifold(s)) disposed in an array under the wound-facing face of thedressing, so as to allow passage of irrigant and/or wound exudatethrough the wound to take place in a controllable linear stream.

Two arrays of inlet pipe(s) and/or outlet pipe(s) (or manifold(s)) underthe wound-facing face of the wound dressing may be aligned parallel toeach other, opposing each other diametrically across the wound, so thatwhen fluid passes between these structures they assist in channellingflow of irrigant and/or wound exudate across the wound in a parallelstream.

Preferably, a plurality of inlet pipe(s) or outlet pipe(s) (ormanifold(s)) is disposed to surround respectively one or more centrallydisposed outlet or inlet pipes. (These may be at the geometric center ofthe backing layer of the wound dressing as hereinbefore defined, ratherthan generally centrally disposed therein.) The purpose is to allowpassage of irrigant and/or wound exudate through the wound to take placein a controllable radial stream. Such a stream applies flow stressradially across the wound bed.

The plurality of inlet and/or outlet pores or apertures respectively inirrigant inlet and/or outlet manifolds, connected in turn to at leastone irrigant inlet pipe(s) and/or outlet pipe(s) under the wounddressing can be considered as equivalent to the above plurality of inletpipe(s) or outlet pipe(s). Again, the purpose is to allow passage ofirrigant and/or wound exudate through the wound to take place in acontrollable linear stream.

As above, such irrigant inlet and/or outlet manifolds may be alignedparallel to each other, opposing each other diametrically across thewound, so that when fluid passes between these structures they assist inchannelling flow of irrigant and/or wound exudate across the wound in aparallel stream. Alternatively they may be arranged in a concentricarrangement or similar wherein an inlet/outlet manifold surrounds acorresponding inlet/outlet manifold.

Preferably, an irrigant inlet and/or outlet manifold with respectively aplurality of inlet and/or outlet apertures is disposed to surroundrespectively at least one more-centrally disposed outlet or inlet pipes.(These may be at the geometric center of the backing layer of the wounddressing as hereinbefore defined, rather than generally centrallydisposed therein.)

Preferably, an irrigant outlet and/or inlet manifold with respectively aplurality of inlet and/or outlet pores or apertures is connectedrespectively to the at least one more-centrally disposed outlet or inletpipes.

The purpose in both cases is to allow passage of irrigant and/or woundexudate through the wound to take place in a controllable radial stream.As above, such a stream applies flow stress radially across the woundbed. As noted above, such irrigant inlet manifolds may befluid-inflatable bodies that lie in the wound in use and formprojections, as described hereinafter in greater detail. These areinflated by admitting irrigant fluid, and they assist in channellingflow of irrigant and/or wound exudate through the wound.

In such cases of radial streaming, the surrounding apertures could be ator near the periphery of the wound-facing face of the dressing, and themore-centrally disposed apertures could be at or near the center.However, each are often disposed regularly or irregularly across thedressing, in the manner of a shower-head, and they are preferablydisposed regularly across it, as this favours a constant flow rate overall parts of the wound bed.

Thus, according to another embodiment of the present invention there isprovided an apparatus for irrigating and/or cleansing wounds,characterised in that it comprises a conformable wound dressing ashereinbefore defined having at least one (and preferably a plurality) ofinlet or outlet apertures more-centrally disposed therein and aplurality of respectively outlet or inlet apertures disposed to surroundthe more-centrally disposed apertures.

The apertures may include the outlets of tubules of an array connectinginto a manifold. More usually, however, in embodiments comprising suchmanifolds, they are formed of porous film or microporous membrane. Theapertures or pores by the wound bed are preferably distributed evenlyover the underside of the dressing and/or over the wound bed in use. Toachieve a relatively high flow rate, and depending on the appropriate ordesired flow rate, of the moving fluid over the wound bed, the aperturesor pores by the wound bed may suitably form of the order of 0.5 to 30%of the area of the wound-facing face of the dressing by the wound bed,such as 0.7 to 10%, e.g. 0.9 to 3%, for example about 1%. They may havean average cross-dimension of 1 to 1000 m, such as 3 to 300 m, e.g. 5 to100 m, for example 6 to 60 m.

To the same end, in certain embodiments of the present invention, thepressure differential across the porous film or microporous membranewith the apertures or pores by the wound bed on the underside of thedressing in use may suitably be of the order of 1 to 500 mmHg, such as 3to 250 mmHg, e.g. 10 to 125 mmHg, for example about 80 mmHg.

Alternatively or additionally, where appropriate there may beprojections, such as bulges or protruberances, and/or where appropriatedepressions, effectively on the wound-facing face of the dressing. Bothwill often run within the wound between the inlet pipe(s) and the outletpipe(s) under the wound-facing face of the wound dressing. (Fluid passesbetween these structures and they assist in channelling flow of irrigantand/or wound exudate through the wound in a controllable stream.)

The projections may have a significantly three-dimensional structure,such as points, bosses, ribs and ridges. Such bosses may be circular,elliptical or polygonal in plan view, such as triangular, rectangular orhexagonal. These may be may be, e.g. an integral net with elongateapertures e.g. formed by fibrillation of an embossed film, sheet ormembrane of a polymeric material or by casting the material. These arepreferably projections in a substantially radiating array under thewound-facing face of the wound dressing. The projections may be disposedregularly or irregularly across the dressing, although they are oftendisposed regularly across it.

Again, the depressions may have a significantly three-dimensionalstructure, such as grooves, channels or conduits. The structures arepreferably in a substantially radial array. Suitably, these may beformed by embossing a sheet, film or membrane. It will be apparent thatany features of inflation of the wound facing face of the dressing maybe used to help direct or guide fluid flow to provide linear flow.Fluid-inflatable bodies that lie in the wound in use may form suchprojections, in particular such inlet manifolds, as describedhereinafter in greater detail. These are inflated by admitting irrigantfluid, and they assist in channelling flow of irrigant and/or woundexudate through the wound in a controllable stream. As noted above, theymay be formed of porous film or microporous membrane. The inflatedmanifolds may have a significantly three-dimensional structure, such aspoints, bosses, ribs and ridges. Such bosses may be circular, ellipticalor polygonal in plan view, such as triangular, rectangular or hexagonal.The backing layer and modules may be of the same or different materials,but each should be of a material that does not absorb aqueous fluidssuch as water, blood, wound exudate, etc. and is soft and resilientlydeformable.

According to another embodiment of the present invention there isprovided a apparatus for irrigating and/or cleansing wounds,characterised in that it comprises a conformable wound dressing ashereinbefore defined having projecting or depressed structures disposedbetween the inlet pipe(s) and the outlet pipe(s) under the wound-facingface of the wound dressing.

In the embodiment of the apparatus that is characterised in that itcomprises means for supplying optionally varying flow velocity, which isoptionally pulsed, to a wound bed for the stimulation of the healing ofthe wound, the relatively high flow rates are typically provided by thedevice for moving fluid through the wound.

The type and/or capacity of a suitable device for moving fluid throughthe wound at the desired velocity will be largely determined by theappropriate or desired fluid flow rate and the flow resistance of theflow path. Suitable devices are indicated below.

As noted hereinbefore, in certain embodiments of the present invention,the flow velocity of the fluid may be constant, but may be varied,preferably cyclically, either randomly or regularly. To achieve this,the present apparatus additionally, where appropriate, comprises asystem which can regulate the pump output to the wound bed under thewound dressing. Preferably such a system is a conventional automated,programmable system which can maintain the wound at or near anappropriate, desired flow stress to the wound bed and regularly orrandomly pulse a flow velocity applied to the wound at any appropriatepoint for this purpose. Such pulsed flow across the wound may beprovided by some types of the device for moving fluid through the wound.

Certain diaphragm pumps described hereinafter in greater detail will beappropriate for this purpose, as are peristaltic pumps, an electricallypulsable valve on the fluid reservoir, and an electromechanicaloscillator directly coupled to the wound dressing.

It will of course be apparent that the apparatus may comprise more thanone of the means described above to induce flow stress. For example theapparatus may have means to vary fluid flow and means to improve linearflow in a desired form.

Pressure Regulation

In relevant embodiments of the present apparatus for aspirating,irrigating and/or cleansing wounds, it is advantageous that itadditionally, where appropriate, comprises a system which can regulatethe pressure on the wound bed, under the wound dressing.

Preferably such a system is a conventional automated, programmablesystem which can maintain the wound at or near an appropriate, desiredstress to the wound bed and optionally tissue surrounding the wound, toan appropriate, desired program while moving fluid over the wound bed atan appropriate, desired rate.

Examples of suitable means for the stimulation of the healing of woundsand tissue adhering well to and growing from the wound bed includeapplying mechanical stimulus to the wound bed and optionally tissuesurrounding the wound via the wound dressing and/or via the fluid underdressing. Examples of suitable ways in which this can in turn beachieved include applying an optionally varying positive and/or negativepressure at any appropriate point for stressing the wound.

The amplitude of the positive and/or negative pressure on the wound bedand optionally tissue surrounding the wound and/or the fluid thereovermay be constant, but more usually is varied, preferably cyclically,either randomly or regularly. Such cyclical variation of the pressureapplied to the wound is effectively the application of an amplitudewaveform at a desired frequency to apply a desired level of stress tothe wound bed and optionally tissue surrounding the wound (it should benoted that application of a varying pressure may cause strain to thesurface of the wound, i.e. deflection of the wound bed, but this isenvisaged in the term stress as used herein).

The desired level and regime of stress to the wound bed and optionallytissue surrounding the wound may be applied conventionally by varyingthe positive and/or negative pressure applied to the wound bed, e.g. by(a) varying the rate of the means for moving fluid over the wound bed asappropriate or desired, e.g. the rate of any pump used to apply positiveor negative pressure to the wound bed at any appropriate point forstressing the wound, (b) bleeding fluids, especially gases, such as airand nitrogen, but not excluding liquids, such as water and saline, orgas in liquid aerosols; and gels into the flowpath in any appropriatepart of the apparatus to vary the pressure applied to the wound to adesired level and/or program, and/or (c) varying the pressure in anyinflatable filler within the wound dressing as appropriate or desired,as described in more detail hereinafter. Preferably, such regular orrandom variation of the positive and/or negative pressure applied to thewound will be effected by conventional process control devices and/orsoftware.

The stimulation of the healing of wounds in certain embodiments of thepresent invention may also be effected by agitation of the wound bedand/or creating intermittent flow and/or turbulence to stimulate thecells. This can be done preferably by regularly or randomly pulsing apositive and/or negative pressure applied to the wound at anyappropriate point for this purpose. Such pulsed variation of thepressure applied to the wound is again effectively the application of anamplitude waveform at a desired frequency to apply a desired level ofstress to the wound bed and optionally tissue surrounding the wound.

Pulsing the pressure on the wound may advantageously also provide ameans to over-ride pain, similar to TENS. The range of variation of thepulsed positive and/or negative pressure applied to the wound will besubstantially less than the maximum levels of pressure referred tobelow, i.e. less than 50% atm and typically significantly lower. Thefrequencies of such pulsed stressing across the wound will besubstantially higher than those of the cycles of positive and/ornegative pressure to the wound bed and optionally tissue surrounding thewound for the stimulation of the healing of wounds referred to above.

The range of variation of the pulsed positive and/or negative pressureapplied to the wound will generally be substantially less than themaximum levels of pressure and than the range of variation in the levelsof pressure referred to below in respect of cycles of positive and/ornegative pressure.

To clarify there are two forms of stress generally envisaged as beinguseful, i.e. those achieved by a slow cycling of pressure, and thoseachieved by a more rapid pulsing of pressures. The range of pressure ina “cycle” is typically significantly greater than that of a “pulse”. Ananalogy is a carrier wave (the cycle) containing the pulse superimposedupon it.

Regularly or randomly pulsing any pressure applied to the wound may beeffected essentially as described hereinbefore in connection with thevariation of the positive and/or negative pressure applied to the wound.Again, such regular or random pulsing of the positive and/or negativepressure applied to the wound may be effected by conventional processcontrol devices and/or software. Such pulsing of any pressure applied tothe wound may be applied as an amplitude modulation of the positiveand/or negative pressure applied to the wound bed and optionally tissuesurrounding the wound, which in turn may be held constant, but moreusually is varied, preferably cyclically, either randomly or regularly(i.e. the carrier wave referred to above may in fact be a constantpositive or negative pressure), but this is generally less preferred.

Where the levels of such pressure above or below atmospheric are heldconstant, this is often achieved in the present apparatus, whereappropriate, by use of a control device that can regulate the pressurein the wound dressing by bleeding fluids, especially gases, such as airand nitrogen, but not excluding liquids, such as water and saline, orgas in liquid aerosols; and gels into the flowpath in any appropriatepart of the apparatus to vary the pressure applied to the wound to adesired level and/or program.

This often results in any device for moving fluid through the wound thatis downstream of the dressing and that applies an overall negativepressure in the wound space, e.g. a vacuum pump, pumping a heterogeneousmixture of liquid wound exudate and irrigant from the wound dressingwith bleed gases, such as air and nitrogen. This can result in pulsingof any pressure applied to the wound.

The pumping rate and the dimensions of the offtake and/or supply tubesmay be adjusted to maintain the desired balance of pulsing pressureamplitude and frequencies on the wound. Preferably such a system is aconventional automated, programmable system which can maintain theappropriate pulse regimen to the wound. Stimulus to the wound bed andoptionally tissue surrounding the wound by applying an optionallyvarying positive and/or negative pressure and agitation of the wound bedto stimulate the cells by regularly or randomly pulsing any pressureapplied to the wound are mutually compatible. They may, as appropriate,be applied alone or together.

Thus, an embodiment of the apparatus for irrigating, stressing and/orcleansing wounds is characterised in that it comprises means forsupplying optionally varying positive and/or negative pressure, which isoptionally pulsed, to a wound bed and optionally tissue surrounding thewound for the stimulation of the healing of the wound.

As noted hereinbefore, in certain embodiments of the present invention,the positive and/or negative pressure on the wound bed and/or the fluidthereover and optionally tissue surrounding the wound may be constant,but more usually is varied, preferably cyclically, either randomly orregularly. Where the pressure on the wound bed and/or the fluidthereover and optionally tissue surrounding is varied, it may be avarying positive or negative pressure, or it may as appropriate varyfrom positive to negative or vice versa, again preferably cyclically,and either randomly or regularly. It may vary about a constant positiveor negative baseline pressure, or less usually about a varying baselinepressure. Examples of maximum levels of such pressure above and belowatmospheric include 50% atm. e.g. between 5 and 40% atm., e.g. between15 and 35% atm.

Examples of suitable frequencies of such regular cycles of pressure forthe stimulation of the healing of wounds include 1 to 48 per 24 hr, suchas 12 to 24 per 24 hr, e.g. 2 to 1 per hr.

Examples of suitable waveforms of such cycles either regularly orrandomly for the stimulation of the healing of wounds include curved,e.g. sinusoidal, random white noise and sawtooth for higher frequencies,and usually square for lower frequencies.

Examples of suitable frequencies of regular pulses for the stimulationof the healing of wounds include 1 to 3000 per min (0.016-50 Hz), e.g.30 to 60 per min, e.g. 3 to 20 per min, i.e. 0.05 to 0.33 Hz, such as 5to 10 per min.

Such pulses may be varying positive or negative pressure pulses, or theymay as appropriate vary from positive to negative or vice versa, againpreferably cyclically, and either randomly or regularly. They may varyabout a constant positive or negative baseline pressure or about avarying baseline pressure. Examples of maximum amplitudes for suchpulses are up to 10 mm Hg above and below the constant positive ornegative baseline pressure, e.g up to 7 mm Hg or up to 3 mm Hg. Examplesof suitable waveforms of such pulses either regularly or randomly forthe stimulation of the healing of wounds include curved, e.g.sinusoidal, random white noise sawtooth, square and a systolic-diastolicasymmetric sawtooth.

Where the amplitude of regular cycles of pressure is modulated bysuperimposed regular pulses for the stimulation of the healing ofwounds, examples of suitable frequencies of the combination includethose where the carrier frequency is 1 to 48 per 24 hours and thesuperimposed frequency of the pressure pulses is 1 to 0.05 Hz, both withthe respective amplitudes noted above. Examples of suitable waveforms ofthe cycles and the superimposed pulses may be regular or random andinclude curved, e.g. sinusoidal, random white noise, sawtooth, squareand a systolic-diastolic asymmetric sawtooth.

Examples of means for applying an optionally varying positive and/ornegative pressure at any appropriate point for stressing the woundand/or regularly or randomly pulsing any pressure applied to the woundfor promoting wound healing, whether applied alone or together, includea wound dressing as hereinbefore defined that comprises one or moreexpandable and contractible modules capable of applying pressure to thewound bed and optionally tissue surrounding the wound at any appropriatepoint for stressing the wound.

Examples of other suitable means of applying mechanical stimulus to thewound by optionally varying positive and/or negative pressure include amagnetic fluid in a chamber or other hollow structure under the backinglayer of the dressing in contact with the wound bed and/or the fluidthereover. A regularly or randomly (preferably cyclically) varyingand/or pulsing external magnetic field is applied to the magnetic fluid.However, such means are generally less favoured.

Thus, one favoured embodiment of the apparatus for irrigating, stressingand/or cleansing wounds is characterised in that it comprises a wounddressing as hereinbefore defined that comprises one or more expandableand contractible modules. Such a module is capable of applying pressureto the wound bed and optionally tissue surrounding the wound at anyappropriate point for stressing the wound. It should be capable ofmaintaining the pressure on the wound bed and/or the fluid thereover andoptionally tissue surrounding the wound at a constant level, but moreusually it should be capable of regularly or randomly (preferablycyclically) varying and/or pulsing the pressure applied to the wound,all at or near an appropriate, desired level of stress to the wound bedand optionally tissue surrounding the wound, to an appropriate, desiredprogram while moving fluid over the wound bed at an appropriate, desiredrate.

Examples of suitable modules capable of applying pressure to the woundbed at any appropriate point for stressing the wound include a module inthe wound dressing may be made of a polymer that can be electricallystimulated to change shape repeatedly at appropriate frequencies. Apreferred module is a fluid-inflatable body that lies in the wound inuse.

Thus, one favoured embodiment of the apparatus for irrigating, stressingand/or cleansing wounds is characterised in that it comprises a wounddressing as hereinbefore defined that comprises one or morefluid-inflatable modules capable of applying pressure to the wound bedat any appropriate point for stressing the wound.

This is capable of maintaining the pressure on the wound bed and/or thefluid thereover at a constant level, but more usually it is also capableof regularly or randomly (preferably cyclically) varying and/or pulsingthe pressure applied to the wound, all at or near an appropriate,desired level of stress to the wound bed, to an appropriate, desiredprogram while moving fluid over the wound bed. The module or modulesis/are (usually cyclically) inflated and deflated by admitting andreleasing fluid. Once the inflatable body has been inflated, it may bedeflated as appropriate or desired, and then reinflated to again apply apositive pressure to the wound, and the cycle may be repeated asappropriate or desired.

Alternatively, it may be partially filled with an elastically resilientmaterial, such as an elastomeric foam, that in its rest state is capableof applying a working pressure to the wound bed. The body may then bedeflated as appropriate or desired, and then reinflated under the actionof its filler material to again apply a positive pressure to the wound,and the cycle may be repeated as appropriate or desired.

Examples of forms of the body that are suitable such expandable andcontractible modules capable of applying pressure to the wound bed atany appropriate point for stressing the wound include fluid-inflatablefillers and fluid-inflatable irrigant inlet manifolds comprised in thedressing, as described hereinafter in greater detail. Where the moduleis a fluid-inflatable filler, examples of suitable fluids include gases,such as air and nitrogen; liquids, such as water and saline; gas inliquid aerosols; and gels such as those described in greater detailhereinafter. Preferred fluids include gases, such as air or nitrogen.Where the module is a fluid-inflatable irrigant inlet manifold comprisedin the dressing as described hereinafter in greater detail, it will bestimulated to change shape as appropriate and optionally at desiredfrequencies by inflation with irrigant, followed as desired bydeflation. Examples of both are included hereinafter.

Examples of such fillers include a substantially flat film, sheet ormembrane, defining a chamber, pouch or other structure of the backinglayer, e.g. of polymer film, which can contain the inflation fluid. Itis provided with an inflation device for moving inflation fluid to thefiller, and is connected to it by an inflation tube which communicateswith its internal space. The inflation device may also serve as adeflation device for moving inflation fluid from the filler, and theinflation tube also serves as a deflation tube.

Alternatively or additionally, where appropriate the filler ashereinbefore defined may have a deflation pipe and a bleed valve towaste, e.g. to a collection bag if a non-gaseous fluid is used. Theinflation device for moving inflation fluid then only serves as aninflation device to apply a positive pressure on the wound bed. Lessusually, the filler may have an inflation device and a deflation device.Where it lies under the backing layer of the wound dressing of theapparatus, the inflation tube may run to the filler within the woundunder the wound-facing face of the wound dressing.

However, the inflation tube may be connected to an inflation pipe thatpasses through the wound-facing face of the backing layer, the point atwhich the inflation pipe passes through the wound-facing face forming arelatively fluid-tight seal. The inflation pipe may be in the form of anaperture, such as a funnel hole, opening, orifice, luer, slot or portfor connection as a female member respectively to a mating end of theinflation tube (optionally or as necessary via means for forming a tube,pipe or hose, or nozzle).

Where the pipe passes through, rather than under the backing layer, thebacking layer may often have a rigid and/or resiliently inflexible orstiff area to resist any substantial play between the or each pipe andthe or each mating tube, or deformation under pressure in any direction.It may often be stiffened, reinforced or otherwise strengthened by aboss projecting distally (outwardly from the wound) around each relevanttube, pipe or hose, or nozzle, hole, opening, orifice, luer, slot orport for connection to a mating end of the inflation tube. Thecomponents may be a push, snap or twist-lock fit with each other. Theminimum calibre of the inflation tube and pipe should be sufficient forthem to permit as rapid inflation and deflation of the filler as isdesired. Suitably the range of cross-dimensions of the bore (i.e.calibre) may be 0.5 to 6 mm, e.g. 1.5 to 2 mm. Each should beresiliently flexible, and preferably soft with good conformability. Thiscan be done for example by forming it of a suitable material, e.g. aresilient thermoplastic.

Examples of suitable inflation device for moving fluid into the fillerinclude pumps. As noted above, the inflation device may also serve as adeflation device for moving inflation fluid from the filler, and theinflation tube also serves as a deflation tube. In such case, the pumpshould be a reversible pump used to increase and decrease the pressureon the wound bed as desired.

Subject to this consideration, the type and/or capacity of the devicewill also be largely determined by (a) the appropriate or desiredpositive or negative pressure to the wound bed, (b) the nature of thefluid, i.e. whether it is a gas, such as air and nitrogen; a liquid,such as water and saline; a gas in liquid aerosol; or a gel; (c) thedesired frequencies and waveforms of such cycles either regularly orrandomly.

The following types of pump may be used to apply positive pressure, asdesired to the filler through an inflation tube which communicates withits internal space: (a) Reciprocating Pumps, such as: (i) Syringe orpiston pumps—providing high pressure and high accuracy; (ii) Diaphragmpumps—where pulsations of one or two flexible diaphragms displace liquidwhile check valves control the direction of the fluid flow e.g.preferably a small portable diaphragm pump; and (b) Rotary pumps, suchas: (i) Centrifugal pumps—with rotating vaned disk attached to a driveshaft moving fluid without pulsation as it spins. The outlet can berestricted without damaging the pump; (ii) Peristaltic pumps—withrollers on a rotor acting on fluid in a tube, e.g. preferably a smallportable peristaltic pump.

Of these, only piston pumps and rotary pumps, such as centrifugal pumpsand peristaltic pumps are readily reversible pumps that may be used toincrease and decrease the pressure on the wound bed as desired. Subjectto this consideration, preferred reversible pumps include a smallportable peristaltic pump.

Preferred non-reversible pumps to be used with a bleed valve to thefiller then include a small portable syringe pump (which is often usedonce and then disposed of) or small portable diaphragm pump, e.g. asphygmometric pump.

Where the module is a fluid-inflatable irrigant inlet manifold comprisedin the dressing as described herein after in greater detail, it will bestimulated to change shape as appropriate and optionally at desiredfrequencies by inflation with irrigant, followed as desired by partialdeflation. It should be noted that the use of such a system is moresuited to a simultaneous system but could be applied to a sequential(i.e. fill/empty cycle) system. When the manifold is inflated it willinfluence the pressure applied to the surface of the wound, and whendeflated the pressure will be reduced (i.e. relative to the baseline ofthe system).

The device for moving fluid through the wound is used to move irrigantto inflate the inlet manifold and apply a positive pressure to the woundbed. As noted hereinafter, the device may suitably be a pump. As notedhereinbefore, the pressure on the wound bed may be constant, but may bevaried, preferably cyclically, either randomly or regularly. To achievethis, the present apparatus, where appropriate, comprises a system thatcan regulate the pump output to the inlet manifold in the wounddressing. Preferably such a system is a conventional automated,programmable system which can maintain the wound at or near anappropriate, desired flow stress to the wound bed to an appropriate,desired program while moving fluid over the wound bed.

As noted hereinbefore, stimulation of the healing of wounds in certainembodiments of the present invention may also be effected by regularlyor randomly pulsing a pressure applied to the wound at any appropriatepoint for this purpose. Such pulsed flow across the wound may beprovided by some types of the device for moving fluid through the wound.Certain diaphragm pumps described hereinafter in greater detail will beappropriate for this purpose, as are certain peristaltic pumps, and anelectromechanical oscillator directly coupled to the wound dressing,would also be suitable.

Suitable materials for such modules (i.e. fillers, manifolds etc) of anytype include synthetic polymeric materials that do not absorb aqueousfluids, such as polyolefins, polysiloxanes and polyesters. They may behydrophilic, and thus also include hydrophilic polyurethanes. They alsoinclude thermoplastic elastomers and elastomer blends, for examplecopolymers, such as ethyl vinyl acetate polystyrene and elastomericpolyurethane formed by solution casting.

Operation of a Typical Apparatus

The operation of a typical apparatus of this type for simultaneousaspiration and irrigation of a wound at a low negative pressure of up to20% atm., more usually up to 10% atm. at the wound, with one pump mayinvolve the following steps. As mentioned previously, the application ofnegative pressure has beneficial effects in wound healing.

Before starting the apparatus for aspirating, irrigating and/orcleansing wounds, the backing layer of the wound dressing is appliedover the wound and conformed to the shape of the bodily part in whichthe wound is to form a relatively fluid-tight seal or closure.

The means for supply flow regulation, connected to a fluid supply tube,such as a regulator, such as a rotary valve, is usually closed, and themeans for aspirate flow regulation (if any), connected to a fluidofftake tube, is opened.

The aspiration pump is started and run to give a negative pressure of upto 50% atm., more usually up to 20% atm., e.g. up to 10% atm. to beapplied applies a vacuum to the interior of the dressing and the wound.

The irrigation pump flow rate and any means for fluid supply regulationare then adjusted, and/or where the aspiration pump and/or theirrigation pump is a variable-speed pump, downstream of the wounddressing, either or both is/are adjusted, to maintain the desiredbalance of fluid at a controlled nominal flow rate and to maintain thedesired negative pressure in the interior of the wound dressing.

Optionally, the means for applying flow stress may then be activated.Suitable forms of means for applying flow stress are set out above. Themeans for applying flow stress may be used to apply flow stressconstantly or periodically, depending on the desired treatment regime.

Alternatively or additionally, the means of applying stress may thenoptionally be activated. Typically the means for applying stresscomprises at least one expandable or contractible module capable ofapplying pressure to the wound bed. In one embodiment such a modulecomprises an inflatable body which lies within the wound in use. Theinflatable body may be used to apply a constant pressure (and hencestress) to the wound or, preferably, may be used to apply a cyclicalpressure. The module may be inflated and deflated be introducing andremoving fluid to the body. Further details of suitable modules andtheir operation are given above.

The apparatus is then run for the desired length of therapy and with thedesired negative pressure and stress regime. After this period, theaspiration pump is stopped.

In one embodiment, the means for supplying physiologically activematerials to the wound is activated at such time as may be appropriate.

In one embodiment, the means for supplying thermal energy to the fluidin the wound in the present apparatus is activated at such time as maybe appropriate. This is often once the pump is running, and the meansfor supply flow regulation is opened.

(These means for supplying thermal energy to the fluid in the wound inthe present apparatus include a heater and/or conductively heatedcomponent of the apparatus flow path upstream of any outlet pipe(s) thatpass through and/or under the wound-facing face of the backing layer ofthe wound dressing, which may supply conducted thermal energy,electromagnetic radiation of an appropriate wavelength, or (less often)convected thermal energy.)

The operation of a typical apparatus for simultaneous aspiration andirrigation of a wound at a low negative pressure of up to 20% atm., moreusually up to 10% atm. at the wound, with two pumps may involve thefollowing steps.

The necessary changes where the mode of operation is at a net positivepressure of e.g. up to 15% atm., more usually up to 10% atm. at thewound will be apparent to the skilled person.

Such a typical apparatus for simultaneous aspiration and irrigation of awound at a low negative pressure of up to 20% atm., more usually up to10% atm. at the wound comprises means for providing simultaneousaspiration and irrigation of the wound which is a combination of (a) afirst device for moving fluid through the wound applied to the aspiratein the fluid offtake tube downstream of and away from the wounddressing, with optional means for aspirate flow regulation, connected toa fluid offtake tube: and (b) a second device for moving fluid throughthe wound applied to the irrigant in the fluid supply tube upstream ofand towards the wound dressing, with optional means for supply flowregulation, connected to a fluid supply tube.

As noted above, either device may be (a) a fixed-throughput device, suchas a fixed-speed pump, which will usually require a discrete means foraspirate flow regulation, connected to a fluid offtake tube, e.g. aregulator, such as a rotary valve, or for irrigant flow regulation,connected to a fluid supply tube, either e.g. a regulator, such as arotary valve, or (b) a variable-throughput device, such as avariable-speed pump, thus effectively forming a combination of a devicefor moving fluid through the wound with means for flow regulation in asingle integer.

As noted above, the apparatus may be (a) a single device for movingfluid through the wound applied to the aspirate in the fluid offtaketube downstream of and away from the wound dressing, in combination with(b) means for supply flow regulation, connected to a fluid supply tube,and (c) means for aspirate flow regulation, connected to a fluid offtaketube.

Before starting the apparatus for aspirating, irrigating and/orcleansing wounds, the backing layer of the wound dressing is appliedover the wound and conformed to the shape of the bodily part in whichthe wound is to form a relatively fluid-tight seal or closure.

Any means for supply flow regulation, connected to a fluid supply tube,such as a regulator, such as a rotary valve, is usually closed, and anymeans for aspirate flow regulation, connected to a fluid offtake tube,is opened.

The aspiration pump is started and run to apply a negative pressure ofup to 50% atm., more usually up to 20% atm., e.g. up to 10% atm., to theinterior of the dressing and the wound.

The irrigation pump is then started, so that both pumps are runningtogether, and any means for supply flow regulation is opened.

The irrigation pump flow rate and any means for fluid supply regulationare then adjusted and/or where the aspiration pump and/or the irrigationpump is a variable-speed pump, either or both is/are is adjusted, tomaintain the desired balance of fluid at a controlled nominal flow rateand to maintain the desired negative pressure in the interior of thewound dressing.

Optionally, the means for applying stress may then be activated, asdescribed above.

In one embodiment, the means for supplying physiologically activematerials to the wound is activated at such time as may be appropriate.

Alternatively or additionally, the means for supplying thermal energy tothe fluid in the wound in the present apparatus is optionally activatedat such time as may be appropriate.

This is often once the pump is running, and the means for supply flowregulation is opened.

(These means for supplying thermal energy to the fluid in the wound inthe present apparatus may include a heater and/or conductively heatedcomponent of the apparatus flow path upstream of any outlet pipe(s) thatpass through and/or under the wound-facing face of the backing layer ofthe wound dressing, which may supply conducted thermal energy,electromagnetic radiation of an appropriate wavelength, or (less often)convected thermal energy.)

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only withreference to the accompanying drawings in which, in pertinentschematics, the means for applying stress to the wound bed is omittedfor clarity. Additionally, the means for supplying conducted thermalenergy which acts on the irrigant fluid in the flowpath upstream of thewound dressing in the fluid supply tube from the irrigant fluidreservoir as close to the wound dressing backing layer as possible isomitted from pertinent schematics for clarity.

FIG. 1 is a schematic view of an apparatus for aspirating, irrigating,and/or cleansing a wound according to embodiments of the presentinvention that have a single device for moving fluid through the woundapplied to the aspirate in the fluid offtake tube downstream of and awayfrom the wound dressing, in combination with means for supply flowregulation, connected to a fluid supply tube, and means for aspirateflow regulation, connected to a fluid offtake tube.

FIG. 2 is a schematic view of another apparatus for aspirating,irrigating, and/or cleansing a wound according to the one embodiment ofthe present invention that has a first device for moving fluid throughthe wound applied to the aspirate in the fluid offtake tube downstreamof and away from the wound dressing, with means for aspirate flowregulation, connected to a fluid offtake tube; and a second device formoving fluid through the wound applied to the irrigant in the fluidsupply tube upstream of and towards the wound dressing.

FIGS. 3 to 7 are cross-sectional views of conformable wound dressings,of certain embodiments of the present invention for aspirating and/orirrigating wounds. In these, FIGS. 3a, 4a, 5a, 6a, and 7a arecross-sectional plan views of the wound dressings, and FIGS. 3b, 4b, 5b,6b, and 7b are cross-sectional side views of the wound dressings.

FIGS. 8 to 10 are various views of inlet and outlet manifold layouts forthe wound dressings of certain embodiments of the present invention forrespectively delivering fluid to, and collecting fluid from, the wound.

FIGS. 11a to d are variants of a two-pump system with essentiallyidentical, and identically numbered, components as in FIG. 2, exceptthat there is a pump bypass loop, (in all except in FIG. 11c ), a filterdownstream of the aspirate collection vessel, and a bleed regulator,such as a rotary valve, connected to the fluid offtake tube or to thewound space, for the regulation of the positive or negative pressureapplied to the wound.

FIGS. 12a to c are variants of a two-pump system with essentiallyidentical, and identically numbered, components as in FIG. 11, exceptthat they have various means for varying the regulation of the positiveor negative pressure applied to the wound.

FIGS. 13 to 26 are cross-sectional views of conformable wound dressings,for aspirating and/or irrigating wounds.

FIG. 27a is a plan view and FIG. 27b a cross-sectional view of a furtherconformable wound dressings for aspirating and/or irrigating wounds.

FIGS. 28 to 30 are cross-sectional views of conformable wound dressings,for aspirating and/or irrigating wounds.

FIGS. 31a and b are variants of a two-pump system with essentiallyidentical, and identically numbered, components as in FIG. 11. However,they have alternative means for handling the aspirate flow to theaspirate collection vessel under negative or positive pressure to thewound in simultaneous aspiration and irrigation of the wound, includingin FIG. 31b a third device for moving fluid into a waste bag.

FIG. 32 is a single-pump system essentially with the omission from theapparatus of FIG. 11 of the second device for moving irrigant fluid intothe wound dressing.

FIG. 33 shows a schematic representation of a simultaneousirrigate/aspirate (SIA) and sequential irrigate/aspirate (SEQ) flowsystem. This system may be used to assess the effects of flow stress inwound healing.

FIG. 34 shows increased WST activity of fibroblasts and thus increasedproliferation of cells in a SIA system with actives from cells beingadded.

FIG. 35 shows a summary of WST activity of fibroblasts in SEQ systemsfor 24 h with or with “cells as actives” component (n=3).

DETAILED DESCRIPTION OF THE EMBODIMENTS

In all of the Figures, whether showing a schematic view of an apparatusfor aspirating, irrigating and/or cleansing a wound according to a firstaspect of the invention, or a view of conformable wound dressings of asecond aspect of the present invention, a biodegradable scaffold may, incertain embodiments, be located under the wound dressing in use incontact with and conforming to the wound bed. It is omitted throughoutfor clarity.

Additionally, in all of the Figures, the integers (12A), the means forsupplying physiologically active agents from cells or tissue to thewound, and (12B), a container that contains a cell or tissue component,may, in alternative embodiments, be replaced by a single fluid reservoir(12).

Referring to FIG. 1, the apparatus (1) for aspirating, irrigating,and/or cleansing wounds comprises a conformable wound dressing (2),having a backing layer (3) which is capable of forming a relativelyfluid-tight seal or closure (4) over a wound (5) and one inlet pipe (6)for connection to a fluid supply tube (7), which passes through thewound-facing face of the backing layer (3) at (8), and one outlet pipe(9) for connection to a fluid offtake tube (10), which passes throughthe backing layer (3) at (11), the points (8), (11) at which the inletpipe and the outlet pipe passes through and/or under the backing layer(3) forming a relatively fluid-tight seal or closure over the wound; theinlet pipe being connected via means for supply flow regulation, here avalve (14), by the fluid supply tube (7) to means for supplyingphysiologically active agents from cells or tissue to the wound, here afluid reservoir (12 a), and in one optional embodiment a container thatcontains a cell or tissue component (12 b) connected to the supply tube(7), and the outlet pipe (9) being connected via means for aspirate flowregulation, here a valve (16) and a fluid offtake tube (10) to waste,e.g. to a collection bag (not shown); a device for moving fluid throughthe wound (5), here a diaphragm pump (18), e.g. preferably a smallportable diaphragm pump, acting on the fluid offtake tube (10) to applya low negative pressure on the wound; and the valve (14) in the fluidsupply tube (7), the valve (16) in the aspiration tube (13), and thediaphragm pump (18), providing means for providing simultaneousaspiration and irrigation of the wound (5), such that fluid may besupplied to fill the flowpath from the fluid reservoir via the containerthat contains the cell or tissue component, in turn connected to asupply tube, fluid supply tube (via the means for supply flowregulation) and moved by the device through the flow path.

The operation of the apparatus is as described hereinbefore. In use, theinlet pipe, means for supply flow regulation, here valve (14), the fluidsupply tube (7) and the container for cells or tissue (12 b) may containphysiologically active components from the cells or tissue intherapeutically active amounts to promote wound healing, and adds suchmaterials into the flowpath.

The supply of such physiologically active materials is here effected tothe wound via the fluid passing through the wound dressing from irrigantin the container that contains the cells or tissue.

Referring to FIG. 2, the apparatus (21) is a variant two-pump systemwith essentially identical, and identically numbered, components as inFIG. 1, except that there is no means such as a valve for supply flowregulation in the fluid supply tube (7) from the fluid reservoir (12 a),and a container that contains a cell or tissue component (12 b)connected to the supply tube (7), and there is a first device for movingfluid through the wound (5), here a diaphragm pump (18 a), e.g.preferably a small portable diaphragm pump, acting on the fluidaspiration tube (13) downstream of and away from the wound dressing toapply a low negative pressure on the wound; with means for negativepressure and/or aspirate flow regulation, here a valve (16) connected tothe vacuum or fluid aspiration tube (13) and a vacuum vessel (aspiratecollection jar) (19); and a second device for moving fluid through thewound (5), here a peristaltic pump (18 b), e.g. preferably a smallportable diaphragm or peristaltic pump, applied to the irrigant in thefluid supply tube (7) upstream of and towards the wound dressing, thefirst device (18 a) and second device (18 b), and the valve (16) in thevacuum or fluid aspiration tube (10), and the diaphragm pump (18 a),providing means for providing simultaneous (or sequential) aspirationand irrigation of the wound (5), such that fluid may be supplied to fillthe flowpath from the fluid reservoir via the fluid supply tube (via themeans for supply flow regulation) and moved by the devices through theflow path.

The operation of the apparatus is as described hereinbefore.

Referring to FIGS. 3 to 6, each dressing is in the form of a conformablebody defined by a microbe-impermeable film backing layer (42) with auniform thickness of 25 micron. It has a wound-facing face, which iscapable of forming a relatively fluid-tight seal or closure over awound. The backing layer (42) extends in use on a wound over the skinaround the wound.

On the proximal face of the backing layer (42) on the overlap, it bearsan adhesive film (not shown), to attach it to the skin sufficiently tohold the wound dressing in place in a fluid-tight seal around theperiphery of the backing layer (42) of the wound dressing.

There is one inlet pipe (46) for connection to a fluid supply tube (notshown), which passes through and/or under the backing layer (42), andone outlet pipe (47) for connection to a fluid offtake tube (not shown),which passes through and/or under the backing layer (42).

Referring to FIGS. 3a and 3b , one form of the dressing is provided witha wound filler (48) under a circular backing layer (42). This comprisesa generally frustroconical, toroidal conformable hollow body, defined bya membrane (49) which is filled with a fluid, here air or nitrogen, thaturges it to the wound shape. The filler (48) may be permanently attachedto the backing layer with an adhesive film (not shown) or byheat-sealing.

The inlet pipe (46) and outlet pipe (47) are mounted centrally in thebacking layer (42) above the central tunnel (50) of the toroidal hollowbody (48) and each passes through the backing layer (42). In otherembodiments the inlet (46) and outlet (47) pipes may pass under thebacking layer (42).

Each extends in pipes (51) and (52) respectively through the tunnel (50)of the toroidal hollow body (48) and then radially in diametricallyopposite directions under the body (48).

This form of the dressing is a more suitable layout for deeper wounds.

Referring to FIGS. 4a and 4b , a more suitable form for shallower woundsis shown.

This comprises a circular backing layer (42) and a circular upwardlydished first membrane (61) with apertures (62) that is permanentlyattached to the backing layer (42) by heat-sealing to form a circularpouch (63).

The pouch (63) communicates with the inlet pipe (46) through a hole(64), and thus effectively forms an inlet pipe manifold that deliversthe circulating or aspirating fluid directly to the wound when thedressing is in use.

An annular second membrane (65) with openings (66) is permanentlyattached to the backing layer (42) by heat-sealing to form an annularchamber (67) with the layer (42).

The chamber (67) communicates with the outlet pipe (47) through anorifice (68), and thus effectively forms an outlet pipe manifold thatcollects the fluid directly from the wound when the dressing is in use.

Referring to FIGS. 5a and 5b , a variant of the dressing of FIGS. 4a and4b that is a more suitable form for deeper wounds is shown.

This comprises a circular backing layer (42) and a filler (69), in theform of an inverted frustroconical, solid integer, here a resilientelastomeric foam, formed of a thermoplastic, or preferably across-linked plastics foam.

It may be permanently attached to the backing layer (42), with anadhesive film (not shown) or by heat-sealing.

A circular upwardly dished sheet (70) lies under and conforms to, but isa separate structure, permanently unattached to, the backing layer (42)and the solid integer (69).

A circular upwardly dished first membrane (71) with apertures (72) ispermanently attached to the sheet (70) by heat-sealing to form acircular pouch (73) with the sheet (70).

The pouch (73) communicates with the inlet pipe (46) through a hole(74), and thus effectively forms an inlet pipe manifold that deliversthe circulating or aspirating fluid directly to the wound when thedressing is in use.

An annular second membrane (75) with openings (76) is permanentlyattached to the sheet (70) by heat-sealing to form an annular chamber(77) with the sheet (70).

The chamber (77) communicates with the outlet pipe (47) through anorifice (78), and thus effectively forms an outlet pipe manifold thatcollects the fluid directly from the wound when the dressing is in use.

Alternatively, where appropriate the dressing may be provided in a formin which the circular upwardly dished sheet (70) functions as thebacking layer and the solid filler (69) sits on the sheet (70) as thebacking layer, rather than under it. The filler (69) is held in placewith an adhesive film or tape, instead of the backing layer (42).

Referring to FIGS. 6a and 6b , a dressing that is a more suitable formfor deeper wounds is shown.

This comprises a circular backing layer (42) and a filler (79), in theform of an inverted generally hemispherical integer, permanentlyattached to the backing layer with an adhesive film (not shown) or byheat-sealing.

Here it is a resilient elastomeric foam or a hollow body filled with afluid, here a gel that urges it to the wound shape. The inlet pipe (46)and outlet pipe (47) are mounted peripherally in the backing layer (42).A circular upwardly dished sheet (80) lies under and conforms to, but isa separate structure, permanently unattached to, the backing layer (42)and the filler (79).

A circular upwardly dished bilaminate membrane (81) has a closed channel(82) between its laminar components, with perforations (83) along itslength on the outer surface (84) of the dish formed by the membrane (81)and an opening (85) at the outer end of its spiral helix, through whichthe channel (82) communicates with the inlet pipe (46), and thuseffectively forms an inlet pipe manifold that delivers the circulatingor aspirating fluid directly to the wound when the dressing is in use.

The membrane (81) also has apertures (86) between and along the lengthof the turns of the channel (82). The inner surface (87) of the dishformed by the membrane (81) is permanently attached at its innermostpoints (88) with an adhesive film (not shown) or by heat-sealing to thesheet (80). This defines a mating closed spirohelical conduit.

At the outermost end of its spiral helix, the conduit communicatesthrough an opening (90) with the outlet pipe (47) and is thuseffectively an outlet manifold to collect the fluid directly from thewound via the apertures (86).

Referring to FIGS. 7a and 7b , one form of the dressing is provided witha circular backing layer (42).

A first (larger) inverted hemispherical membrane (92) is permanentlyattached centrally to the layer (42) by heat-sealing to form ahemispherical chamber (94) with the layer (42).

A second (smaller) concentric hemispherical membrane (93) within thefirst is permanently attached to the layer (42) by heat-sealing to forma hemispherical pouch (95).

The pouch (95) communicates with the inlet pipe (46) and is thuseffectively an inlet manifold, from which pipes (97) radiatehemispherically and run to the scaffold and/or wound bed to end inapertures (98). The pipes (97) deliver the aspirating fluid directly tothe scaffold and/or wound bed via the apertures (98).

The chamber (94) communicates with the outlet pipe (47) and is thuseffectively an outlet manifold from which tubules (99) radiatehemispherically and run to the scaffold and/or wound bed to end inopenings (100). The tubules (99) collect the fluid directly from thewound via the openings (100).

Referring to FIGS. 8a to 8d , one form of the dressing is provided witha square backing layer (42) and first tube (101) extending from theinlet pipe (46), and second tube (102) extending from the outlet pipe(47) at the points at which they pass through the backing layer, to runover the scaffold and/or wound bed.

These pipes (101) and (102) have a blind bore with orifices (103) and(104) along the pipes (101) and (102).

These pipes (101) and (102) respectively form an inlet pipe or outletpipe manifold that delivers the aspirating fluid directly to thescaffold and/or wound bed or collects the fluid directly from the woundrespectively via the orifices.

In FIGS. 8a and 8d , one layout of each of the pipes (101) and (102) asinlet pipe and outlet pipe manifolds is a spiral.

In FIG. 8b , the layout is a variant of that of FIGS. 8a and 8b , withthe layout of the inlet manifold (101) being a full or partial torus,and the outlet manifold (102) being a radial pipe.

Referring to FIG. 8c , there is shown another suitable layout in whichthe inlet manifold (101) and the outlet manifold (102) run alongsideeach other over the scaffold and/or wound bed in a boustrophedicpattern, i.e. in the manner of ploughed furrows.

Referring to FIGS. 9a to 9d , there are shown other suitable layouts fordeeper wounds, which are the same as shown in FIGS. 8a to 8d . Thesquare backing layer (42) however has a wound filler (110) under, andmay be permanently attached to, the backing layer (42), with an adhesivefilm (not shown) or by heat-sealing, which is an inverted hemisphericalsolid integer, here a resilient elastomeric foam, formed of athermoplastic, preferably a cross-linked plastics foam.

Under the latter is a circular upwardly dished sheet (111) whichconforms to, but is a separate structure, permanently unattached to, thesolid filler (110). Through the sheet (111) pass the inlet pipe (46) andthe outlet pipe (47), to run over the scaffold and/or wound bed. Thesepipes (101) and (102) again have a blind bore with orifices (103) and(104) along the pipes (101) and (102).

Alternatively (as in FIGS. 5a and 5b ), where appropriate the dressingmay be provided in a form in which the circular upwardly dished sheet(111) functions as the backing layer and the solid filler (110) sits onthe sheet (42) as the backing layer, rather than under it. The filler(110) is held in place with an adhesive film or tape, instead of thebacking layer (42).

In FIGS. 10a to 10c , inlet and outlet manifolds for the wound dressingsfor respectively delivering fluid to, and collecting fluid from, thewound, are formed by slots in and apertures through layers permanentlyattached to each other in a stack.

Thus, in FIG. 10a there is shown an exploded isometric view of an inletmanifold and outlet manifold stack (120) of five square coterminousthermoplastic polymer layers, being first to fifth layers (121) to(125), each attached with an adhesive film (not shown) or byheat-sealing to the adjacent layer in the stack (120).

The topmost (first) layer (121) (which is the most distal in thedressing in use) is a blank square capping layer.

The next (second) layer (122), shown in FIG. 10b out of the manifoldstack (120), is a square layer, with an inlet manifold slot (126)through it. The slot (126) runs to one edge (127) of the layer (122) forconnection to a mating end of a fluid inlet tube ((not shown), andspreads into four adjacent branches (128) in a parallel array withspaces therebetween.

The next (third) layer (123) is another square layer, with inletmanifold apertures (129) through the layer (123) in an array such thatthe apertures (129) are in register with the inlet manifold slot (126)through the second layer (122) (shown in FIG. 10b ).

The next (fourth) layer (124), shown in FIG. 10c out of the manifoldstack (120), is another square layer, with inlet manifold apertures(130) through the layer (124) in an array such that the apertures (130)are in register with the apertures (129) through the third layer (123).

It also has an outlet manifold slot (131) through it.

The slot (131) runs to one edge (132) of the layer (124) on the oppositeside of the manifold stack (120) from the edge (127) of the layer (122),for connection to a mating end of a fluid outlet tube (not shown).

It spreads into three adjacent branches (133) in a parallel array in thespaces between the apertures (130) in the layer (124) and in registerwith the spaces between the apertures (129) in the layer (122).

The final (fifth) layer (125) is another square layer, with inletmanifold apertures (134) through the layer (125) in an array such thatthe apertures (134) are in register with the inlet manifold apertures(130) through the fourth layer (124) (in turn in register with theapertures (129) through the third layer (123). It also has outletmanifold apertures (135) in the layer (125) in an array such that theapertures (135) are in register with the outlet manifold slot (131) inthe fourth layer (124).

It will be seen that, when the layers (121) to (125) are attachedtogether to form the stack (120), the topmost (first) layer (121), theinlet manifold slot (126) through the second layer (122), and the thirdlayer (123) cooperate to form an inlet manifold in the second layer(122), which is in use is connected to a mating end of a fluid inlettube (not shown).

The inlet manifold slot (126) through the second layer (122), and theinlet manifold apertures (129), (130) and (134) through the layers(123), (124) and (125), all being mutually in register, cooperate toform inlet manifold conduits through the third to fifth layers (123),(124) and (125) between the inlet manifold in the second layer (122) andthe proximal face (136) of the stack (120).

The third layer (121), the outlet manifold slot (131) through the fourthlayer (124), and the fifth layer (125) cooperate to form an outletmanifold in the fourth layer (124), which is in use is connected to amating end of a fluid outlet tube (not shown).

The outlet manifold slot (131) through the fourth layer (124), and theoutlet manifold apertures (135) through the fifth layer (125), beingmutually in register, cooperate to form outlet manifold conduits thoughthe fifth layer (125) between the outlet manifold in the fourth layer(124) and the proximal face (136) of the stack (120).

Referring to FIG. 11a , the apparatus (21) is a variant two-pump systemwith essentially identical, and identically numbered, components as inFIG. 2.

Thus, there is a means for supply flow regulation, here a valve (14) inthe fluid supply tube (7) from the fluid reservoir (12B), and a firstdevice for moving fluid through the wound (5), here a fixed-speeddiaphragm pump (18A), e.g. preferably a small portable diaphragm pump,acting not on the fluid aspiration tube (13), but on an air aspirationtube (113) downstream of and away from an aspirate collection vessel(19) to apply a low negative pressure on the wound through the aspiratecollection vessel (19); with a second device for moving fluid throughthe wound (5), here a fixed-speed peristaltic pump (18B), e.g.preferably a small portable peristaltic pump, applied to the irrigant inthe fluid supply tube (7) upstream of and towards the wound dressing,the first device (18A) and second device (18B), and the valve (14) inthe fluid supply tube (7), providing means for providing simultaneousaspiration and irrigation of the wound (5), such that fluid may besupplied to fill the flowpath from the fluid reservoir via the fluidsupply tube (via the means for supply flow regulation) and moved by thedevices through the flow path.

Key differences as compared with FIG. 2 are that: the second device,pump (18B) acts, not on the fluid aspiration tube (13), but on an airaspiration tube (113) downstream of and away from an aspirate collectionvessel (19); and there is no means for aspirate flow regulation, e.g. avalve connected to the fluid offtake tube (10). Since first device (18A)and second device (18B) are fixed-speed, the valve (14) in the fluidsupply tube (7) provides the sole means for varying the irrigant flowrate and the low negative pressure on the wound.

The following extra features are present: The second device, thefixed-speed peristaltic pump (18B), is provided with means for avoidingover-pressure, in the form of a bypass loop with a non-return valve(115). The loop runs from the fluid supply tube (7) downstream of thepump (18B) to a point in the fluid supply tube (7) upstream of the pump(18B).

A pressure monitor (116) connected to the fluid offtake tube (10) has afeedback connection to a bleed regulator, here a motorized rotary valve(117) on a bleed tube (118) running to and centrally penetrating the topof the aspirate collection vessel (19). This provides means for holdingthe low negative pressure on the wound at a steady level.

A filter (119) downstream of the aspirate collection vessel (19)prevents passage of gas- (often air-) borne particulates, includingliquids and micro-organisms, from the irrigant and/or exudate thatpasses into the aspirate collection vessel (19) into the first device(18A), whilst allowing the carrier gas to pass through the airaspiration tube (113) downstream of it to the first device (18A). Theoperation of the apparatus is as described hereinbefore

Referring to FIG. 11b , this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 11adownstream of point A. The bleed tube (118) runs to the air aspirationtube (113) downstream of the filter (119), rather than into the aspiratecollection vessel (19). This provides means for holding the low negativepressure on the wound at a steady level. The operation of the apparatusis as described hereinbefore

Referring to FIG. 11c , this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 11aupstream of point B. The second device (18B) is a variable-speed pump,and the valve (14) in the fluid supply tube (7) is omitted. The seconddevice (18B) is the sole means for varying the irrigant flow rate andthe low negative pressure on the wound. The operation of the apparatusis as described hereinbefore

Referring to FIG. 11d , this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 11adownstream of point B.

The pressure monitor (116) is connected to a monitor offtake tube (120)and has a feedback connection to the bleed regulator, motorized rotaryvalve (117) on a bleed tube (118) running to the monitor offtake tube(120). This provides means for holding the low negative pressure on thewound at a steady level. The operation of the apparatus is as describedhereinbefore

Referring to FIG. 12a , this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 11adownstream of point B.

The pressure monitor (116) is connected to a monitor offtake tube (120)and has a feedback connection to a means for aspirate flow regulation,here a motorized valve (16) in the fluid offtake tube (10) upstream ofthe filter (119).

This provides means for aspirate flow regulation and for holding the lownegative pressure on the wound at a steady level. The operation of theapparatus is as described hereinbefore

Referring to FIG. 12b , this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 12adownstream of point B in FIG. 11a . The pressure monitor (116) isconnected to a monitor offtake tube (120) and has a feedback connectionto a means for aspirate flow regulation, here a motorized valve (16), inthe fluid offtake tube (10) upstream of the aspirate collection vessel(19).

This provides means for aspirate flow regulation and for holding the lownegative pressure on the wound at a steady level. The operation of theapparatus is as described hereinbefore

Referring to FIG. 12c , this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 12adownstream of point B in FIG. 11a . The pressure monitor (116) isconnected to a monitor offtake tube (120) and has a feedback connectionto a variable-speed first device (18A), here a variable-speed pump,downstream of the filter (119), and the valve (16) in the fluid offtaketube (10) is omitted. This provides means for aspirate flow regulationand for holding the low negative pressure on the wound at a steadylevel. The operation of the apparatus is as described hereinbefore.

Referring to FIGS. 13 to 15, these forms of the dressing are providedwith a wound filler (348) under a circular backing layer (342).

This comprises respectively a generally downwardly domed or toroidal, oroblately spheroidal conformable hollow body, defined by a membrane (349)which is filled with a fluid, here air or nitrogen, that urges it to thewound shape.

The filler (348) is permanently attached to the backing layer via a boss(351), which is e.g. heat-sealed to the backing layer (342).

An inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)are mounted centrally in the boss (351) in the backing layer (342) abovethe hollow body (348). The inflation inlet pipe (350) communicates withthe interior of the hollow body (348), to permit inflation of the body(348). Though such inflation of the hollow body (348) the stress appliedto the wound can be varied by varying the pressure within the hollowbody (348). The inlet pipe (346) extends in a pipe (352) effectivelythrough the hollow body (348). The outlet pipe (347) extends radiallyimmediately under the backing layer (342).

In FIG. 13, the pipe (352) communicates with an inlet manifold (353),formed by a membrane (361) with apertures (362) that is permanentlyattached to the filler (348) by heat-sealing.

It is filled with foam (363) formed of a suitable material, e.g. aresilient thermoplastic. Preferred materials include reticulatedfiltration polyurethane foams with small apertures or pores.

In FIG. 14, the outlet pipe (347) communicates with a layer of foam(364) formed of a suitable material, e.g. a resilient thermoplastic.Again, preferred materials include reticulated filtration polyurethanefoams with small apertures or pores.

The filler (348) is permanently attached to the backing layer via a boss(351), which is e.g. heat-sealed to the backing layer (342).

In all of FIGS. 13, 14 and 15, in use, the pipe (346) ends in one ormore openings that deliver the irrigant fluid directly to the scaffoldand/or wound bed over an extended area.

Similarly, the outlet pipe (347) effectively collects the fluid radiallyfrom the wound periphery when the dressing is in use.

Referring to FIG. 16, the dressing is also provided with a wound filler(348) under a circular backing layer (342).

This also comprises a generally toroidal conformable hollow body,defined by a membrane (349) which is filled with a fluid, here air ornitrogen, that urges it to the wound shape.

The filler (348) may be permanently attached to the backing layer (342)via a first boss (351) and a layer of foam (364) formed of a suitablematerial, e.g. a resilient thermoplastic. Again, preferred materialsinclude reticulated filtration polyurethane foams with small aperturesor pores.

The first boss (351) and foam layer (364) are respectively heat-sealedto the backing layer (342) and the boss (351).

An inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)are mounted centrally in the first boss (351) in the backing layer (342)above the toroidal hollow body (348).

The inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)respectively each extend in a pipe (353), (354) and (355) through acentral tunnel (356) in the hollow body (348) to a second boss (357)attached to the toroidal hollow body (348).

The pipe (353) communicates with the interior of the hollow body (348),to permit inflation of the body (348).

The pipe (354) extends radially through the second boss (357) tocommunicate with an inlet manifold (352), formed by a membrane (361).

This is permanently attached to the filler (348) by heat-sealing in theform of a reticulated honeycomb with openings (362) that deliver theirrigant fluid directly to the scaffold and/or wound bed over anextended area.

The pipe (355) collects the fluid flowing radially from the wound centerwhen the dressing is in use.

This form of the dressing is a more suitable layout for deeper wounds

In FIG. 17, the dressing is similar to that of FIG. 16, except that thetoroidal conformable hollow body, defined by a membrane (349), is filledwith a fluid, here a solid particulates, such as plastics crumbs orbeads, rather than a gas, such as air or an inert gas, such as nitrogenor argon.

The inflation inlet pipe (350) and pipe (353) are omitted from thecentral tunnel (356).

Examples of contents for the body (348) also include gels, such assilicone gels or preferably cellulosic gels, for example hydrophiliccross-linked cellulosic gels, such as Intrasite™ cross-linked materials.Examples also include aerosol foams, and set aerosol foams, e.g.CaviCare™ foam.

Referring to FIGS. 18 and 19, another form for deeper wounds is shown.

This comprises a circular backing layer (342) and a lobed chamber (363)in the form of a deeply indented disc much like a multiple Maltese crossor a stylised rose.

This is defined by an upper impervious membrane (361) and a lower porousfilm (362) with apertures (352) that deliver the irrigant fluid directlyfrom the scaffold and/or wound bed over an extended area.

A number of configurations of the chamber (363) are shown, all of whichare able to conform well to the wound bed by the arms closing in andpossibly overlapping in insertion into the wound.

In a particular design of the chamber (363), shown lowermost, one of thearms is extended and provided with an inlet port at the end of theextended arm. This provides the opportunity for coupling and decouplingthe irrigant supply remote from the dressing and the wound in use.

An inlet pipe (346) and outlet pipe (347) are mounted centrally in aboss (351) in the backing layer (342) above the chamber (363). The inletpipe (346) is permanently attached to, and communicate with the interiorof, the chamber (363), which thus effectively forms an inlet manifold.The space above the chamber (363) is filled with a loose gauze packing(364).

In FIG. 18, the outlet pipe (347) collects the fluid from the interiorof the dressing from just under the wound-facing face of the backinglayer (342).

A variant of the dressing of FIG. 18 is shown in FIG. 19. The outletpipe (347) is mounted to open at the lowest point of the space above thechamber (363) into a piece of foam (374).

In FIG. 20, the dressing is similar to that of FIG. 13, except that theinlet pipe (352) communicates with an inlet manifold (353).

The latter is formed by a membrane (361) with apertures (362), over theupper surface of the generally downwardly domed wound hollow filler(348), rather than through it.

In FIG. 21, the generally downwardly domed annular wound hollow filleris omitted.

In FIG. 22, the dressing is similar to that of FIG. 14, with theaddition of an inlet manifold (353), formed by a membrane (361) withapertures (362), over the lower surface of the generally downwardlydomed annular wound hollow filler.

Referring to FIG. 23, another form for deeper wounds is shown. An inletpipe (346) and outlet pipe (347) are mounted centrally in a boss (351)in the backing layer (342) above a sealed-off foam filler (348).

The inlet pipe (346) is permanently attached to and passes through thefiller (348) to the scaffold and/or wound bed. The outlet pipe (347) isattached to and communicates with the interior of, a chamber (363)defined by a porous foam attached to the upper periphery of the filler(348). The chamber (363) thus effectively forms an outlet manifold.

In FIG. 24, the foam filler (348) is only partially sealed-off. Theinlet pipe (346) is permanently attached to and passes through thefiller (348) to the scaffold and/or wound bed. The outlet pipe (347) isattached to and communicates with the interior of the foam of the filler(348). Fluid passes into an annular gap (349) near the upper peripheryof the filler (348) into the foam, which thus effectively forms anoutlet manifold.

FIGS. 25 and 26 show dressings in which the inlet pipe (346) and outletpipe (347) pass through the backing layer (342).

In FIG. 25, they communicate with the interior of a porous bag filler(348) defined by a porous film (369) and filled with elasticallyresilient plastics bead or crumb.

In FIG. 26, they communicate with the wound space just below a foamfiller (348). The foam (348) may CaviCare™ foam, injected and formed insitu around the pipes (346) and (347).

Referring to FIG. 27, another form for deeper wounds is shown. Thiscomprises a circular, or more usually square or rectangular backinglayer (342) and a chamber (363) in the form of a deeply indented discmuch like a multiple Maltese cross or a stylised rose.

This is defined by an upper impervious membrane (361) and a lower porousfilm (362) with apertures (364) that deliver the irrigant fluid directlyto the wound bed over an extended area, and thus effectively forms aninlet manifold. Three configurations of the chamber (363) are shown inFIG. 27b , all of which are able to conform well to the wound bed by thearms closing in and possibly overlapping in insertion into the wound.

The space above the chamber (363) is filled with a wound filler (348)under the backing layer (342). This comprises an oblately spheroidalconformable hollow body, defined by a membrane (349) that is filled witha fluid, here air or nitrogen, that urges it to the wound shape. Aninflation inlet pipe (350) is mounted centrally in a first boss (351) inthe backing layer (342) above the hollow body (348). The inflation inletpipe (350) communicates with the interior of the hollow body (348), topermit inflation of the body (348). Again, this inflation of the hollowbody (348) is conveniently a means to apply stress to the wound.

A moulded hat-shaped boss (351) is mounted centrally on the upperimpervious membrane (361) of the chamber (363). It has three internalchannels, conduits or passages through it (not shown), each with entryand exit apertures. The filler (348) is attached to the membrane (361)of the chamber (363) by adhesive, heat welding or a mechanical fixator,such as a cooperating pin and socket.

An inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)pass under the edge of the proximal face of the backing layer (342) ofthe dressing.

They extend radially immediately under the filler (348) and over themembrane (361) of the chamber (363) to each mate with an entry aperturein the boss (351).

An exit to the internal channel, conduit or passage through it thatreceives the inflation inlet pipe (350) communicates with the interiorof the hollow filler (348), to permit inflation.

An exit to the internal channel, conduit or passage that receives theinlet pipe (346) communicates with the interior of the chamber (363) todeliver the irrigant fluid via the chamber (363) to the wound bed overan extended area.

Similarly, an exit to the internal channel, conduit or passage thatreceives the outlet pipe (347) communicates with the space above thechamber (363) and under the wound filler (348), and collects flow ofirrigant and/or wound exudate radially from the wound periphery.

Referring to FIG. 28, one form of the dressing comprises a circularsheet (70) that lies under a circular backing layer (72) and ispermanently attached to a boss (81), which is e.g. heat-sealed to thebacking layer (72).

An annular layer of foam (74) formed of a suitable material, e.g. aresilient thermoplastic, preferably a reticulated filtrationpolyurethane foam with small apertures or pores, spaces the sheet (70)from the backing layer and surrounds the boss (81).

A downwardly dished membrane (75) with openings (76) is permanentlyattached to the sheet (70) by heat-sealing to form a chamber (77) withthe sheet (70).

An inlet pipe (76) and outlet pipe (77) are mounted centrally in theboss (81) and pass through the backing layer (72).

The inlet pipe (76) is made of a polyurethane tubular core (not shown)surrounded by an annulus of resistive conductive material, such as oneof the resistive alloys noted hereinbefore, which generates thermalenergy when a voltage drop is applied over it. It is connected to a cell(78), shown schematically, which applies a voltage drop over it.

The inlet pipe (76) communicates with the interior of the chamber (77),which thus forms an inlet manifold that distributes heated fluiddirectly to the wound when the dressing is in use.

The outlet pipe (77) extends radially immediately under the backinglayer (3) and communicates with the inner face of the layer of foam(74), which forms an outlet manifold.

This form of the dressing is a more suitable layout for shallow wounds

Another form of dressing is shown in FIG. 29. An inlet pipe (76) andoutlet pipe (77) are mounted centrally in a boss (81) in, and passthrough a backing layer (72). An oblately hemispheroidal filler (88)with an annular groove (89) may be permanently attached to the pipes(76) and (77).

It is formed of a suitable material, e.g. a resilient thermoplasticfoam, preferably a reticulated filtration polyurethane foams with smallapertures or pores.

An annular electrical heat pad (90) is mounted around the boss (81) ontop of the backing layer (3), which is capable of conducting heat to thewound (5) through the irrigant.

It may be in the form of non-woven or woven fabric, such as a wovenlayer or sheet of carbon fibres or a fabric, such as a woven layer orsheet made essentially of carbonised acrylate, such as polyacrylonitrileand copolymers thereof, which generate thermal energy when a voltagedrop is applied over it.

Alternatively, it may be an electrically insulating flat sheet ormembrane substrate that has an electrically resistive but conductiveprinted circuit on it. It is connected to a cell (78), shownschematically, which applies a voltage drop over it.

The inlet pipe (76) communicates with the wound space at the lowestpoint of the filler (88). The outlet pipe (77) communicates with thegroove (89), and effectively collects the fluid from the wound peripherywhen the dressing is in use.

This form of the dressing is a more suitable layout for deeper wounds.

In FIG. 30, an inlet pipe (76) and outlet pipe (77) are mountedcentrally in a boss (81) in, and pass through a backing layer (72). Anoblately spheroidal conformable hollow body (78) is defined by amembrane (79) which is filled with a fluid, here air or nitrogen, thaturges it to the wound shape, and is permanently attached to the pipes(76) and (77).

It is formed of a suitable material, e.g. a resilient thermoplastic,preferably a reticulated filtration polyurethane foam with smallapertures or pores.

The inflation inlet pipe (350) communicates with the interior of thehollow body (78), to permit inflation of the body (78). The inlet pipe(76) extends through the hollow body (78). The outlet pipe (77)communicates with an outlet manifold formed by a series of radialapertures in a foam disc immediately under the backing layer, thatcollects the fluid from the wound periphery when the dressing is in use.

An electrical heater (90) is mounted under the boss (81) on top of thebacking layer (3), which is transparent to radiant heat, and so permitits transmission to the wound (5) through the irrigant.

It may be in the form of a near infrared radiant heater which generatesthermal energy when a voltage drop is applied over it. It is connectedto a cell (78), shown schematically, which applies a voltage drop overit.

Referring to FIG. 31a , this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 11adownstream of point B, and alternative means for handling the aspirateflow to the aspirate collection vessel under negative or positivepressure to the wound. The pressure monitor (116) is connected to amonitor offtake tube (120) and has a feedback connection to avariable-speed first device (18A), here a variable-speed pump, upstreamof the aspirate collection vessel (19), and the filter (119) and the airaspiration tube (113) are omitted. This provides means for aspirate flowregulation and for holding the low negative pressure on the wound at asteady level. The operation of the apparatus is as describedhereinbefore.

Referring to FIG. 31b , this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 11adownstream of point A, and alternative means for handling the aspirateflow to the aspirate collection vessel under negative or positivepressure to the wound. The pressure monitor (116) is omitted, as is thefeedback connection to a variable-speed first device (18A), here avariable-speed pump, downstream of the aspirate collection vessel (19)and the filter (119).

A third device (18C), here a fixed-speed pump, provides means for movingfluid from the aspirate collection vessel (19) into a waste bag (19A).The operation of the apparatus is as described hereinbefore.

Referring to FIG. 32, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 11aupstream of point A.

It is a single-pump system essentially with the omission from theapparatus of FIG. 11A of the second device for moving irrigant fluidinto the wound dressing. The operation of the apparatus is as describedhereinbefore.

Referring to FIG. 33, a suitable apparatus for assessing the effect offlow stress on cells in a simulated wound is shown.

A pump (18 b) pumps irrigation fluid from a reservoir (12) through a 3way valve (14) which can be configured to allow normal continuous flow,emptying of the test chamber (400) under vacuum, or emptying of the testchamber (400) at atmospheric pressure.

The irrigation fluid passes into a test chamber (400) described in moredetail later. The aspirate leaving the test chamber (400) passes into awaste reservoir (19).

A source of vacuum (18A) manifolds the system at a vacuum (950 mbar) anddraws the aspirate into the waste reservoir (19). An additional pump(401) recycles the aspirate from the waste reservoir (19) back to theirrigant reservoir (12). This is suitable for an in vitro system, butwould generally be unsuitable for treatment of a patient where theaspirate would contain quantities of deleterious compounds. In suchcases a system wherein the vacuum (401) is used would be suitable as thewaste aspirant is not recycled.

EXAMPLES

The use of the apparatus of the present invention will now be describedby way of example only in the following Examples:

Example 1

Removal of wound proteins and derivatives with a two-pump apparatus.

In this example, a gelatine sheet laid in a cavity wound modelrepresents wound proteins and derivatives to be removed by the two-pumpapparatus. The dressing is essentially identical with that in FIG. 18,i.e. it comprises a circular backing layer and a lobed chamber in theform of a deeply indented disc much like a multiple Maltese cross or astylised rose, defined by an upper impervious membrane and a lowerporous film with apertures that deliver the irrigant fluid directly fromthe wound bed over an extended area.

A two-pump system was set up essentially as in FIG. 2, with (a) anirrigant dispensing bottle—1000 ml Schott Duran, connected to (b) aperistaltic pump (Masterflex) for irrigant delivery, and associatedpower supply and supply tube, (c) a diaphragm vacuum pump (Schwarz) foraspiration, and associated power supply and offtake tube, connected to(d) a vacuum vessel (aspirate collection jar)—Nalgene 150 mlpolystyrene, (e) each pump being connected to a dressing consisting ofthe following elements: (i) a wound contacting element, comprising alobed bag with low porosity ‘leaky’ membrane scaffold on the lowersurface, impermeable film on the top, and a foam spacer between the twolayers to allow free flow of irrigant solution; (ii) a space fillingelement, comprising a reticulated, open-cell foam (black reticulatedfoam, Foam Techniques) 30 mm thick, 60 mm diameter; (iii) an occlusiveadhesive coated polyurethane backing layer top film (Smith & NephewMedical) with acrylic pressure sensitive adhesive; (iv) two tubespassing under the occlusive top film, and sealed to prevent leakage ofgas or liquid: one tube centrally penetrating the top film of thewound-contacting element to deliver irrigant into the chamber formed bythis film and the porous element; the other tube of approximately equallength to remove aspirate with the opening positioned just above the topfilm of the wound contacting element.

Preparation of Gelatine Sheet

A 20% aqueous solution of gelatine was prepared by weighing gelatineinto a glass jar and making it up to the required weight with deionizedwater. The jar was placed in an oven (Heraeus), at set temperature 85°C. After 60 minutes the jar was removed from the oven and shaken, toencourage mixing. Petri dishes were partially filled with 10 gquantities of the gelatine solution and placed in a fridge (LEC, settemperature: 4° C.) to set for at least 1 hour. Final thickness of thegelatine slab was ˜5 mm. Petri dishes containing the gelatine slabs wereremoved from the fridge at least 2 hours before use.

Preparation of Test Equipment and Materials

Irrigant solution (deionized water) and the Perspex wound model werepre-conditioned in an oven (Gallenkamp) at set temperature 37° C., forat least 4 hours before use.

For each test, a freshly prepared gelatine slab was removed from a Petridish and weighed.

The Perspex wound model was then removed from the oven and the gelatineslab placed at the bottom of the cavity. Application of the dressing tothe wound model was as follows: (a) the wound contacting element wascarefully placed over the gelatine slab; (b) the foam filler was placedon top of this with the irrigant and aspirate tubes running centrally tothe top of the cavity (the foam filler was slit to the center tofacilitate this); (c) the side entry port, pre-threaded onto the tubes,was adhesively bonded to the upper surface of the wound model blockusing an acrylic pressure sensitive adhesive; (d) the top adhesivecoated film was applied over all of the elements and pressed down togive a seal on all sides, and especially around the tube entry/exitpoint.

Application of the dressing to the wound model was the same for alltests performed. All tubing used was the same for each experiment (e.g.material, diameter, length).

Simultaneous Irrigation & Aspiration

A schematic diagram of the system used in the experiment is shown below.For the experiment most of the apparatus (not including the pumps, powersupply, and connecting tubing to and from the pumps) was placed in anoven (Gallenkamp, set temperature: 37° C.), on the same shelf.

Before starting the irrigation pump a vacuum was drawn on the system tocheck that the dressing and tube connections were substantially airtight(the pumping system was controlled to give a pressure at the vacuumvessel of approximately −75 mmHg before opening the system up to includethe dressing).

Once system integrity had been confirmed, the irrigation pump wasstarted (nominal flow rate: 50 ml/hr), i.e. both pumps running together.Timing of the experiment was started when the advancing water frontwithin the irrigant tube was observed to have reached the top of thedressing.

After 60 minutes, the irrigation pump was stopped, shortly followed bythe vacuum (aspiration) pump.

Aspirate liquid collected in the vacuum jar was decanted into a glassjar. The vacuum jar was rinsed with ˜100 ml of deionized water and thisadded to the same glass jar.

The aspirate solution was placed in an oven (Heraeus, set temperature:130° C.) and dried to constant weight.

Sequential Irrigation & Aspiration

The experimental set up was as for the simultaneousirrigation/aspiration experiment.

Before starting the experiment a vacuum was pulled on the system tocheck that the dressing and tube connections were substantiallyairtight. The pumping system was controlled to give a pressure at thevacuum vessel of approximately −75 mmHg before opening the system up toinclude the dressing. Once system integrity had been confirmed, theirrigation pump was started (nominal rate: 186 ml/hr) and run until theadvancing water front in the irrigant tube was observed to have reachedthe top of the dressing.

The pump was temporarily stopped at this point whilst the vacuum linewas sealed (using a tube clamp) and the vacuum pump stopped.

Timing of the experiment was from the point the irrigation pump wasrestarted. The pump was run until 50 ml of irrigant had entered thewound model (just over 16 minutes at the rate of 186 ml/hr). At thispoint the irrigant pump was stopped.

It was observed that during the filling phase of sequential filling andflushing, air trapped in the model wound cavity caused the top film ofthe dressing to inflate substantially, to a point approaching failure.

After a further ˜44 minutes (60 minutes from the start of theexperiment) the vacuum pump was started and the tube clamp on theaspirate line removed. The wound model was aspirated for 5 minutes.Towards the end of this period a small leak was introduced into the topfilm of the dressing to maximize the amount of fluid drawn from thewound model (it was observed that as the pressure differential betweenthe wound model cavity and the vacuum jar reduced to zero, the flow ofaspirate also tended to slow. Introducing a small leak re-establishedthe pressure differential and the flow of aspirate out of the cavity).

Results and Conclusions

Simultaneous Irrigation & Aspiration Reference Aspirate Recovery ofConcentration of gelatine in number recovered (g) gelatine (%) aspiratedfluid (% w/w) 1 48.81 79.33 3.27 2 45.64 72.30 3.18 3 48.84 68.05 2.76Mean 47.76 73.22 3.07

Sequential Irrigation & Aspiration Cycle Reference Aspirate Recovery ofConcentration of gelatine in number recovered (g) gelatine (%) aspiratedfluid (% w/w) 1 32.08 19.59 1.23 2 34.09 18.35 1.07 3 33.90 10.77 0.64Mean 33.36 16.24 0.98

Simultaneously irrigating and aspirating the wound model removed more ofthe gelatine placed at the base of the wound model cavity thansequentially filling and emptying the cavity, even though the amount ofliquid entering the wound and the duration of the experiment were thesame in both cases.

Simultaneously irrigating and aspirating also removed more fluid fromthe model wound.

Example 2

The combination of simultaneous fluid flow (irrigation) and aspiration(under reduced pressure) on wound bed fibroblasts compared with theexposure of wound bed fibroblasts to repeated fill-empty cycles of fluidflow and aspiration.

An apparatus of the present invention was constructed essentially as inFIG. 33, which is an apparatus where an irrigant is deliveredcontinually to the wound bed and the resultant wound exudate/fluidmixture is at the same time continually aspirated from the wound.Alternative systems are known where the wound is subjected to repeatediteration of a cycle of fluid delivery followed by a period ofaspiration under reduced pressure.

The apparatus comprised a surrogate wound chamber (Minucells perfusionchamber) in which normal diploid human fibroblasts were cultured on 13mm diameter (Thermanox polymer) cover slips retained in a two partsupport (Minucells Minusheets). Tissues present in the healing woundthat must survive and proliferate were represented by the cells withinthe chamber. Nutrient medium (DMEM with 10% FCS with 1% Buffer All) tosimulate an irrigant fluid/wound exudate mixture, was pumped from areservoir into the lower aspect of the chamber where it bathed thefibroblasts and was removed from the upper aspect of the chamber andreturned to a second reservoir. The wound chamber was maintained at lessthan atmospheric pressure by means of a vacuum pump in line with thecircuit.

The pumps for the circuit were peristaltic pumps acting on silicone (orequivalent) elastic tubing. The circuit was exposed to a vacuum of nomore than 10% atmospheric pressure, 950 mbar and atmospheric pressurevaried up to a maximum value of 1044 mbar. The internal diameter of thetubing was 1.0 mm. A total volume for the circuit including the chamberand the reservoir of between 50 and 220 ml was used. The flow rates usedwere at a number of values between 0.1 ml min⁻¹ and 2.0 ml⁻¹ min⁻¹.

An experiment was conducted that simulated conditions that are notuncommon for healing wounds whereby a fluid was delivered to the woundbed and the application of a vacuum was used to remove the mixture offluid and exudate to a waste reservoir.

An air bleed fluid control valve was additionally positioned in thecircuit so that on opening the air bleed occurred for a time and closedthe fluid flow, the simulated irrigant fluid/wound exudate mixture wasevacuated from the chamber and the fibroblasts were maintained under anegative pressure relative to the atmosphere. This represents anempty/fill system.

Results and Conclusions

The following results were obtained for a circuit comprising a woundchamber as above containing a total volume of nutrient media (154 ml)pumped at a flow rate of 0.2 ml min-1 and where vacuum was set at 950mbar and where atmospheric pressure varied up to a maximum value of 1044mbar. The wound chamber and media were held at 37° C. for 25 hours. Inone set of wound chambers continuous flow was maintained. In a secondset of chambers 6 cycles of empty/fill were performed with each fill orempty phase lasting 1 hour.

In controls where empty/fill system with 6×cycles of 1 hour empty/1 hourfill over a total of 25 hours, the survival and growth of thefibroblasts is inhibited.

However, when the nutrient medium flow in the first circuit is deliveredcontinually to the Minucells chamber and the resultant nutrient mediumis at the same time continually aspirated from the Minucells chamberunder vacuum was set at 950 mbar and where atmospheric pressure variedup to a maximum value of 1044 mbar, the fibroblasts survive andproliferate to a greater extent during a 25 hour period than the controlempty/fill circuits

Mean relative level of cell activity* Conditions after 25 hours.Baseline cell activity prior 100% to introduction to wound chamber Fillempty 6 cycles  93% Continuous flow 143% *Cell activity measured with aWST (Tetrazolium based mitochondrial dehdrogenase activity assay). Datanormalised to fibroblasts seeded onto coverslips with normal nutrientmedia baseline activity

The combination of continuous fluid flow at 0.2 ml min⁻¹ and waste fluidremoval under vacuum of no more than 10% atmospheric pressure, 950 mbarand atmospheric pressure varied up to a maximum value of 1044 mbar,enhances the cell response necessary for wound healing more than thefill empty fill pattern under vacuum.

Example 3

Removal of wound proteins and heating a wound with a two-pump apparatus.

In this example, a gelatine sheet laid in a cavity wound modelrepresents wound proteins and derivatives to be removed by the two-pumpapparatus.

The dressing is essentially identical with that in FIG. 28, i.e. a formof the dressing with an inlet pipe surrounded by an annulus of resistiveconductive material, which is connected to a cell via a circuit with acurrent control and a switch, and generates thermal energy when avoltage drop is applied over it by the cell.

The inlet pipe communicates with the interior of an inlet manifold thatdistributes heated fluid directly to the wound when the dressing is inuse.

A two-pump system is set up essentially as in FIG. 2, with an irrigantdispensing bottle—1000 ml Schott Duran, connected to a peristaltic pump(Masterflex) for irrigant delivery, and associated power supply andsupply tube, a diaphragm vacuum pump (Schwarz) for aspiration, andassociated power supply and offtake tube, connected to a vacuum vessel(aspirant collection jar)—Nalgene 150 ml polystyrene, each pump beingconnected to a dressing consisting of the following elements:wound-contacting element, comprising a lobed bag with low porosity‘leaky’ membrane scaffold on the lower surface, impermeable film on thetop, and a foam spacer between the two layers to allow free flow ofirrigant solution, a space filling element, comprising a reticulated,open-cell foam (black reticulated foam, Foam Techniques) 30 mm thick, 60mm diameter, an occlusive adhesive coated polyurethane backing layer topfilm (Smith & Nephew Medical) with acrylic pressure sensitive adhesive,two tubes passing under the occlusive top film, and sealed to preventleakage of gas or liquid: one tube centrally penetrating the top film ofthe wound-contacting element to deliver irrigant into the chamber formedby this film and the porous element; the other tube of approximatelyequal length to remove aspirant with the opening positioned just abovethe top film of the wound contacting element.

Pressure sensor in wound model cavity

Temperature sensor in wound model cavity

Preparation of Gelatine Sheet:

A 20% aqueous solution of gelatine is prepared by weighing gelatine intoa glass jar and making it up to the required weight with deionizedwater. The jar is placed in an oven (Heraeus), at set temperature 85° C.

After 60 minutes the jar is removed from the oven and shaken, toencourage mixing. Petri dishes are partially filled with 10 g quantitiesof the gelatine solution and placed in a fridge (LEC, set temperature:4° C.) to set for at least 1 hour. Final thickness of the gelatine slabis ˜5 mm. Petri dishes containing the gelatine slabs are removed fromthe fridge at least 2 hours before use.

Preparation of Test Equipment and Materials

Irrigant solution (deionized water) and the Perspex wound model arepre-conditioned in an oven (Gallenkamp) at set temperature 37° C., forat least 4 hours before use.

For each test, a freshly prepared gelatine slab is removed from a Petridish and weighed. The Perspex wound model is then removed from the ovenand the gelatine slab placed at the bottom of the cavity. Application ofthe dressing to the wound model is as follows: (i) the wound contactingelement is carefully placed over the gelatine slab; (ii) the foam filleris placed on top of this with the irrigant and aspirant tubes runningcentrally to the top of the cavity (the foam filler is slit to thecenter to facilitate this); (iii) the side entry port, pre-threaded ontothe tubes, is adhesively bonded to the upper surface of the wound modelblock using an acrylic pressure sensitive adhesive; (iv) the topadhesive coated film is applied over all of the elements and presseddown to give a seal on all sides, and especially around the tubeentry/exit point.

Application of the dressing to the wound model is the same for all testsperformed. All tubing used is the same for each experiment (e.g.material, diameter, length).

Simultaneous Irrigation & Aspiration

A schematic diagram of the system used in the experiment is shown below.For the experiment most of the apparatus (not including the pumps, powersupply, and connecting tubing to and from the pumps) is placed in anoven (Gallenkamp, set temperature: 37° C.), on the same shelf.

Before starting the irrigation pump a vacuum is drawn on the system tocheck that the dressing and tube connections are substantially airtight.

The pumping system is controlled to give a pressure at the vacuum vesselof approximately −75 mmHg before opening the system up to include thedressing).

Once system integrity has been confirmed, the irrigation pump is started(nominal flow rate: 50 ml/hr), i.e. both pumps running together.

The means for supplying thermal energy to the fluid in the wound in thepresent apparatus is then activated, i.e. the switch is closed, so thata voltage drop is applied over the annulus of resistive conductivematerial, and it generates thermal energy, which is conducted to theirrigant liquid passing through the inlet pipe into the manifoldchamber. The current control is adjusted to maintain a temperature atthe wound bed under the wound-facing face of the backing layer of thewound dressing at a constant level throughout the experiment of 36 to38° C.

Timing of the experiment is started when the advancing water frontwithin the irrigant tube is observed to have reached the top of thedressing.

After 60 minutes, the means for supplying thermal energy to the fluid inthe wound in the present apparatus is deactivated, i.e. the switch isopened, so that a voltage drop is no longer applied over the annulus ofresistive conductive material.

The irrigation pump is stopped, shortly followed by the vacuum(aspiration) pump. Aspirant liquid collected in the vacuum jar isdecanted into a glass jar. The vacuum jar is rinsed with ˜100 ml ofdeionized water and this added to the same glass jar. The aspirantsolution is placed in an oven (Heraeus, set temperature: 130° C.) anddried to constant weight.

Sequential Irrigation & Aspiration

The experimental set up is as for the simultaneous irrigation/aspirationexperiment. Before starting the experiment a vacuum is pulled on thesystem to check that the dressing and tube connections are substantiallyairtight.

The pumping system is controlled to give a pressure at the vacuum vesselof approximately −75 mmHg before opening the system up to include thedressing.

Once system integrity has been confirmed, the irrigation pump is started(nominal rate: 186 ml/hr) and the means for supplying thermal energy tothe fluid in the wound in the present apparatus is then activated, i.e.the switch is closed, so that a voltage drop is applied over the annulusof resistive conductive material. The current control is adjusted tomaintain a temperature at the wound bed under the wound-facing face ofthe backing layer of the wound dressing at a constant level throughoutthe experiment of 36 to 38° C.

The pump is run until the advancing water front in the irrigant tube isobserved to have reached the top of the dressing.

The pump is temporarily stopped at this point whilst the vacuum line issealed (using a tube clamp) and the vacuum pump stopped.

Timing of the experiment is from the point the irrigation pump isrestarted. The pump is run until 50 ml of irrigant has entered the woundmodel (just over 16 minutes at the rate of 186 ml/hr). At this point themeans for supplying thermal energy to the fluid in the wound in thepresent apparatus is deactivated, i.e. the switch is opened, so that avoltage drop is no longer applied over the annulus of resistiveconductive material. The irrigant pump is stopped.

It is observed that during the filling phase of sequential filling andflushing, air trapped in the model wound cavity caused the top film ofthe dressing to inflate substantially, to a point approaching failure.

After a further ˜44 minutes (60 minutes from the start of theexperiment) the vacuum pump is started and the tube clamp on theaspirant line removed. The wound model is aspirated for 5 minutes.

Towards the end of this period a small leak is introduced into the topfilm of the dressing to maximize the amount of fluid drawn from thewound model (it is observed that as the pressure differential betweenthe wound model cavity and the vacuum jar reduced to zero, the flow ofaspirant also tended to slow. Introducing a small leak re-establishedthe pressure differential and the flow of aspirant out of the cavity).

Results and Conclusions

Using the present apparatus with its means for supplying thermal energyto the fluid in the wound, one is able to achieve and maintain atemperature at the wound bed under the wound-facing face of the backinglayer of the wound dressing at a constant level of 36 to 38° C., whilesimultaneously irrigating and aspirating the wound model withprogrammable fluid movement.

Simultaneously irrigating and aspirating also removes more of thesurrogate wound protein sheet placed at the base of the wound modelcavity than sequentially filling and emptying the cavity, even thoughthe amount of liquid entering the wound and the duration of theexperiment are the same in both cases. Simultaneously irrigating andaspirating also removes more fluid from the model wound.

Example 4

The combination of simultaneous warmed fluid flow (irrigation) andaspiration (under reduced pressure) on wound bed fibroblasts comparedwith the exposure of wound bed fibroblasts to repeated fill-empty cyclesof warmed fluid flow and aspiration.

An apparatus of the present invention was constructed essentially as inFIG. 33, which is an apparatus where an irrigant or fluid of some natureis delivered continually to the wound bed and the resultant woundexudate/fluid mixture is at the same time continually aspirated from thewound. Alternative systems are known where the wound is subjected torepeated iteration of a cycle of fluid delivery followed by a period ofaspiration under reduced pressure.

The apparatus comprised a surrogate wound chamber (Minucells perfusionchamber) in which normal diploid human fibroblasts were cultured on 13mm diameter (Thermanox polymer) cover slips retained in a two partsupport (Minnucells Minusheets). Tissues present in the healing woundthat must survive and proliferate were represented by the cells withinthe chamber. Nutrient medium (DMEM with 10% FCS with 1% Buffer All) tosimulate an irrigant fluid/wound exudate mixture, was pumped from areservoir into the lower aspect of the chamber where it bathed thefibroblasts and was removed from the upper aspect of the chamber andreturned to a second reservoir. The wound chamber was maintained at lessthan atmospheric pressure by means of a vacuum pump in line with thecircuit.

The pumps for the circuit were peristaltic pumps acting on silicone (orequivalent) elastic tubing.

The circuit was exposed to a vacuum of no more than 10% atmosphericpressure, 950 mbar and atmospheric pressure varied up to a maximum valueof 1044 mbar. The internal diameter of the tubing was 1.0 mm. A totalvolume for the circuit including the chamber and the reservoir ofbetween 50 and 220 ml was used. The flow rates used were at a number ofvalues between 0.1 ml min⁻¹ and 2.0 ml⁻¹ min⁻¹.

First circuit also comprised: upstream of the wound chamber, a heatexchanger such that the temperature of the nutrient media bathing thecells reaches between 35° C. and 37° C.

Experiments were conducted that simulated conditions not uncommon forhealing wounds whereby the chamber simulating the wound was placed in aroom temperature environment (simulating the low temperatures oftenexperienced in wounds where blood flow is poor), additional chambersheated such that the cells reaches between 35° C. and 37° C.

An experiment was conducted that simulated conditions that are notuncommon for healing wounds whereby a fluid was delivered to the woundbed and the application of a vacuum is used to remove the mixture offluid and exudate to a waste reservoir. An air bleed fluid control valvewas additionally positioned in the circuit so that on opening the airbleed occurred for a time and closed the fluid flow, the simulatedirrigant fluid/wound exudate mixture was evacuated from the chamber andthe fibroblasts were maintained under a negative pressure relative tothe atmosphere. This represents an empty/fill system. 6 cycles ofempty/fill were performed with each fill or empty phase lasting 1 hour.

Apparatus was also constructed essentially as in FIG. 33, but whereeither (a) it was was operated as an empty/fill system with 6×cycles of1 hour empty/1 hour fill over a total of 25 hours, or (b) the heatexchanger is omitted, so that the nutrient flow bathing the cells doesnot reach between 35° C. and 37° C. and remains at between 18° C. and20° C.

Results and Conclusions

The following results were obtained for a circuit comprising a woundchamber as above containing a total volume of nutrient media (154 ml)pumped at a flow rate of 0.2 ml min⁻¹ and where vacuum was set at 950mbar and where atmospheric pressure varied up to a maximum value of 1044mbar. The wound chamber and media were held at 37° C. for 25 hours. Inone set of wound chambers continuous flow was maintained. In a secondset of chambers 6 cycles of empty/fill were performed with each fill orempty phase lasting 1 hour.

In controls where either (a) it was operated as an empty/fill systemwith 6×cycles of 1 hour empty/1 hour fill over a total of 25 hours, (b)the heat exchanger unit is omitted; the survival and growth of thefibroblasts is inhibited.

However, when the nutrient medium flow in the first circuit is (a) isdelivered continually to the minucell chamber and the resultant nutrientmedium is at the same time continually aspirated from the minucellchamber under vacuum was set at 950 mbar and where atmospheric pressurevaried up to a maximum value of 1044 mbar, (b) And passes through a heatexchanger so that the temperature of the nutrient media bathing thecells reaches between 35° C. and 37° C.; the fibroblasts survive andproliferate to a greater extent during a 25 hour period than the controlempty/fill circuits.

Mean of cell activity* Conditions after 25 hours. N = 3 Baseline cellactivity prior to 0.25 introduction to wound chamber Continuous flow(SIA) flow at 0.39 room temperature Continuous flow (SIA) plus heat 0.45(37° C.) Fill empty 6 cycles at room 0.24 temperature Fill empty 6cycles plus heat 0.38 (37° C.) *Cell activity measured with a WST(Tetrazolium based mitochondrial dehdrogenase activity assay).

The combination of heat (37° C.) and continuous fluid flow at 0.2 mlmin⁻¹ with waste fluid removal under vacuum of no more than 10%atmostpheric pressure, 950 mbar and atmospheric pressure varied up to amaximum value of 1044 mbar, enhances the cell response necessary forwound healing more than the fill empty fill pattern under vacuum.

Example 5

Removal of adherent bacteria and debris with a two-pump apparatus.

In this example, a culture medium sheet containing nutritionalsupplements with an adherent bacterial culture of Staphylococcus aureuson its top surface is laid in a cavity wound model to represent adherentbacteria and debris on a wound bed to be removed by the two-pumpapparatus.

The dressing is essentially identical with that in FIG. 18, i.e. itcomprises a circular backing layer and a lobed chamber in the form of adeeply indented disc much like a multiple Maltese cross or a stylisedrose, defined by an upper impervious membrane and a lower porous filmwith apertures that deliver the irrigant fluid directly from the woundbed over an extended area.

The irrigant supplied to the wound dressing under a negative pressure onthe wound bed contains a therapeutically active amount of anantibacterial agent, selected from chlorhexidine, povidone iodine,triclosan, metronidazole, cetrimide and chlorhexidine acetate.

A two-pump system is set up essentially as in FIG. 2, with an irrigantdispensing bottle—1000 ml Schott Duran, connected to a peristaltic pump(Masterflex) for irrigant delivery, and associated power supply andsupply tube, a diaphragm vacuum pump (Schwarz) for aspiration, andassociated power supply and offtake tube, connected to a vacuum vessel(aspirant collection jar)—Nalgene 150 ml polystyrene each pump beingconnected to a dressing consisting of the following elements:wound-contacting element, comprising a lobed bag with low porosity‘leaky’ membrane scaffold on the lower surface, impermeable film on thetop, and a foam spacer between the two layers to allow free flow ofirrigant solution, a space filling element, comprising a reticulated,open-cell foam (black reticulated foam, Foam Techniques) 30 mm thick, 60mm diameter, an occlusive adhesive coated polyurethane backing layer topfilm (Smith & Nephew Medical) with acrylic pressure sensitive adhesive,two tubes passing under the occlusive top film, and sealed to preventleakage of gas or liquid: one tube centrally penetrating the top film ofthe wound-contacting element to deliver irrigant into the chamber formedby this film and the porous element; the other tube of approximatelyequal length to remove aspirant with the opening positioned just abovethe top film of the wound contacting element.

Preparation of Agar Culture Medium Sheet With Adherent Staphylococcusaureus Culture

An aqueous solution of agar culture medium is prepared by weighing agarculture medium containing nutritional supplements into a glass jar andmaking it up to the required weight with deionized water. The jar isplaced in an oven (Heraeus), at a set temperature. After 60 minutes thejar is removed from the oven and shaken, to encourage mixing.

Petri dishes are partially filled with 10 g quantities of the culturemedium and placed in a fridge (LEC, set temperature: 4° C.) to set forat least 1 hour.

Final thickness of the culture medium sheet is ˜5 mm. Petri dishescontaining the culture medium sheet are removed from the fridge at least2 hours before use. The culture medium sheet in the Petri dishes is theninoculated with Staphylococcus aureus.

Each is then placed in an incubator at a set temperature.

After the culture has covered more than 50% of the agar surface thedishes are removed from the incubator.

They are place in a fridge, and removed from the fridge at least 2 hoursbefore use.

Preparation of Test Equipment and Materials

Irrigant solution (deionized water containing a therapeuticallyeffective amount of an antibacterial agent, selected from chlorhexidine,povidone iodine, triclosan, metronidazole, cetrimide and chlorhexidineacetate) and the Perspex wound model are pre-conditioned in an oven(Gallenkamp) at set temperature 37° C., for at least 4 hours before use.

For each test, a freshly prepared culture medium sheet with adherentStaphylococcus aureus culture is removed from a Petri dish and weighed.The Perspex wound model is then removed from the oven and the culturemedium sheet with adherent Staphylococcus aureus culture placed at thebottom of the cavity. Application of the dressing to the wound model isas follows: (i) the wound contacting element is carefully placed overthe culture medium sheet with adherent Staphylococcus aureus culture,(ii) the foam filler is placed on top of this with the irrigant andaspirant tubes running centrally to the top of the cavity (the foamfiller is slit to the center to facilitate this), (iii) the side entryport, pre-threaded onto the tubes, is adhesively bonded to the uppersurface of the wound model block using an acrylic pressure sensitiveadhesive, (iv) the top adhesive coated film is applied over all of theelements and pressed down to give a seal on all sides, and especiallyaround the tube entry/exit point

Application of the dressing to the wound model is the same for all testsperformed. All tubing used is the same for each experiment (e.g.material, diameter, length).

Simultaneous Irrigation & Aspiration

For the experiment most of the apparatus (not including the pumps, powersupply, and connecting tubing to and from the pumps) is placed in anoven (Gallenkamp, set temperature: 37° C.), on the same shelf.

Before starting the irrigation pump a vacuum is drawn on the system tocheck that the dressing and tube connections are substantially airtight.

The pumping system is controlled to give a pressure at the vacuum vesselof approximately −75 mmHg before opening the system up to include thedressing). Once system integrity has been confirmed, the irrigation pumpis started (nominal flow rate: 50 ml/hr), i.e. both pumps runningtogether. Timing of the experiment is started when the advancing waterfront within the irrigant tube is observed to have reached the top ofthe dressing.

After 60 minutes, the irrigation pump is stopped, shortly followed bythe vacuum (aspiration) pump. Aspirant liquid collected in the vacuumjar is decanted into a glass jar. The vacuum jar is rinsed with ˜100 mlof deionized water and this added to the same glass jar. The aspirantsolution is then assayed for the Staphylococcus aureus quantity present.

Sequential Irrigation & Aspiration

The experimental set up is as for the simultaneous irrigation/aspirationexperiment. Before starting the experiment a vacuum is pulled on thesystem to check that the dressing and tube connections are substantiallyairtight. The pumping system is controlled to give a pressure at thevacuum vessel of approximately −75 mmHg before opening the system up toinclude the dressing. Once system integrity has been confirmed, theirrigation pump is started (nominal rate: 186 ml/hr) and run until theadvancing water front in the irrigant tube is observed to have reachedthe top of the dressing.

The pump is temporarily stopped at this point whilst the vacuum line issealed (using a tube clamp) and the vacuum pump stopped.

Timing of the experiment is from the point the irrigation pump isrestarted. The pump is run until 50 ml of irrigant has entered the woundmodel (just over 16 minutes at the rate of 186 ml/hr). At this point theirrigant pump is stopped.

It is observed that during the filling phase of sequential filling andflushing, air trapped in the model wound cavity caused the top film ofthe dressing to inflate substantially, to a point approaching failure.

After a further ˜44 minutes (60 minutes from the start of theexperiment) the vacuum pump is started and the tube clamp on theaspirant line removed. The wound model is aspirated for 5 minutes.Towards the end of this period a small leak is introduced into the topfilm of the dressing to maximize the amount of fluid drawn from thewound model (it is observed that as the pressure differential betweenthe wound model cavity and the vacuum jar reduced to zero, the flow ofaspirant also tended to slow. Introducing a small leak re-establishedthe pressure differential and the flow of aspirant out of the cavity).

Aspirant liquid collected in the vacuum jar is decanted into a glassjar. The vacuum jar is rinsed with ˜100 ml of deionized water and thisadded to the same glass jar. The aspirant solution is then assayed forthe Staphylococcus aureus quantity present.

Results and Conclusions

Simultaneously irrigating and aspirating the wound model removes orkills more of the adherent Staphylococcus aureus on the culture mediumsheet placed at the base of the wound model cavity than sequentiallyfilling and emptying the cavity, even though the amount of liquidentering the wound and the duration of the experiment are the same inboth cases. Simultaneously irrigating and aspirating also removes morefluid from the model wound.

Example 6

The combination of simultaneous fluid flow (irrigation) with aspiration(under reduced pressure) and actives (PDGF-bb) on wound bed fibroblastscompared with the exposure of wound bed fibroblasts to repeatedfill-empty cycles of fluid flow and aspiration.

An apparatus of the present invention was constructed essentially as inFIG. 33 which is an apparatus where an irrigant or fluid of some natureis delivered continually to the wound bed and the resultant woundexudate/fluid mixture is at the same time continually aspirated from thewound.

Alternative systems are known where the wound is subjected to repeatediteration of a cycle of fluid delivery followed by a period ofaspiration under reduced pressure.

The apparatus comprised a surrogate wound chamber (Minucells perfusionchamber) in which normal diploid human fibroblasts were cultured on 13mm diameter (Thermanox polymer) cover slips retained in a two partsupport (Minnucells Minusheets). Tissues present in the healing woundthat must survive and proliferate were represented by the cells withinthe chamber. Nutrient medium (DMEM with 10% FCS with 1% Buffer All) tosimulate an irrigant fluid/wound exudate mixture, was pumped from areservoir into the lower aspect of the chamber where it bathed thefibroblasts and was removed from the upper aspect of the chamber andreturned to a second reservoir. The wound chamber was maintained at lessthan atmospheric pressure by means of a Vacuum pump in line with thecircuit.

The pumps for the circuit were peristaltic pumps acting on silicone (orequivalent) elastic tubing. The circuit was exposed to a vacuum of nomore than 10% atmospheric pressure, 950 mbar and atmospheric pressurevaried up to a maximum value of 1044 mbar. The internal diameter of thetubing was 1.0 mm. A total volume for the circuit including the chamberand the reservoir of between 100 and 220 ml was used. The flow ratesused were at a number of values between 0.1 ml min⁻¹ and 2.0 ml⁻¹ min⁻¹.

An experiment was conducted that simulated conditions that are notuncommon for healing wounds whereby a fluid was delivered to the woundbed and the application of a vacuum is used to remove the mixture offluid and exudate to a waste reservoir. An air bleed fluid control valvewas additionally positioned in the circuit so that on opening the airbleed occurred for a time and closed the fluid flow, the simulatedirrigant fluid/wound exudate mixture was evacuated from the chamber andthe chamber left empty and the fibroblasts were maintained under anegative pressure relative to the atmosphere. This represents anempty/fill system, 6 cycles of empty/fill were performed with each fillor empty phase lasting 1 hour.

An experiment was conducted using the following 2 scenarios:

Apparatus was constructed essentially as in FIG. 30 but where (a)continuous flow simultaneous aspirate irrigate system with (b) materialbeneficial to wound healing (PDGF-bb) was present in the nutrient flowbathing the cells.

Apparatus was also constructed essentially as in FIG. 30 but (a) it wasoperated as an empty/fill system with 6×cycles of 1 hour empty/1 hourfill over a total of 25 hours with (b) the material beneficial to woundhealing (PDGF-bb) was present, in the nutrient flow bathing the cells.

Results and Conclusions

The following results were obtained for a circuit comprising a woundchamber as above containing a total volume of nutrient media (104 ml)pumped at a flow rate of 0.2 ml min⁻¹, and where vacuum was set at 950mbar and where atmospheric pressure was varied up to a maximum value of1044 mbar. The wound chamber and media were held at 37° C. for 25 hours.In one set of wound chambers continuous flow was maintained. In a secondset of chambers 6 cycles of empty/fill were performed with each fill orempty phase lasting 1 hour.

In controls (a) operated as empty/fill with 6 cycles of 1 hour empty/1hour fill, and (b) where PDGF-bb is present, the survival and growth offibroblasts is inhibited compared to the continuous flow systems.

Where flow circuits consists of (a) continuous flow (SIA) and (b)PDGF-bb is present, the survival and growth of fibroblasts is enhancedto a greater level than empty/fill plus PDGF-bb

Mean of cell activity* Conditions after 25 hours. Continuous flow (SIA)plus 0.34 active (PDGF-bb) Fill empty 6 cycles plus active 0.22(PDGF-bb) *Cell activity measured with a WST (Tetrazolium basedmitochondrial dehdrogenase activity assay).

The combination of actives (PDGF-bb) and continuous fluid flow at 0.2 mlmin⁻¹ with waste fluid removal under a vacuum of no more than 10%atmospheric pressure, enhances the cell response necessary for woundhealing more than the fill empty system (+PDGF-bb).

Example 7

The combination of simultaneous fluid flow (irrigation) and aspiration(under reduced pressure) versus the exposure of wound bed fibroblasts torepeated fill-empty cycles of fluid flow and aspiration.

An apparatus was constructed essentially as in FIG. 33.

The apparatus may be used to represent an apparatus of the presentinvention where an irrigant fluid is delivered continually to the woundbed and the resultant wound exudate/fluid mixture is at the same timecontinually aspirated from the wound under reduced pressure and ispumped to waste, or an alternative system where the wound is subjectedto repeated iteration of a cycle of fluid delivery followed by a periodof aspiration to waste under reduced pressure.

For reasons of economy, aspiration was not carried out to waste, but theaspirate was re-circulated.

The apparatus comprised a surrogate wound chamber (Minucells perfusionchamber) in which normal diploid human fibroblasts were cultured on 13mm diameter nylon disks retained in a two part support (MinucellsMinusheets). Tissues present in the wound bed that must survive andproliferate in the healing process were represented by the cells withinthe chamber. A bioscaffold matrix (consisting of a Vicryl mesh (90:10polyglycollic lactic acid) coated with extracellular matrix) was placedin close proximity to the wound bed fibroblasts and all parts wereretained between the Minucells Minisheets within the surrogate woundchamber.

Nutrient medium (DMEM with 1% Buffer All) to simulate an irrigantfluid/wound exudate mixture, was pumped from a reservoir (reservoir 1)into the lower aspect of the chamber where it bathed the fibroblasts andwas removed from the upper aspect of the chamber to a second reservoir(reservoir 1) and thence returned to reservoir 1.

The circuit also comprised a heat exchanger upstream of the woundchamber (not shown), such that the temperature of the nutrient mediabathing the cells reaches between 35° C. and 37° C.

In use as an apparatus of the present invention where an irrigant fluidis delivered continually to the wound bed and the resultant woundexudate/fluid mixture is at the same time continually aspirated from thewound under reduced pressure and is pumped to waste:

The wound chamber was maintained at less than atmospheric pressure bymeans of a vacuum pump, by which the circuit was exposed to a vacuum ofno more than 10% atmospheric pressure, 950 mbar and atmospheric pressurevaried up to a maximum value of 1044 mbar, and which also served as afirst device downstream of the surrogate wound for moving fluid awayfrom the wound.

The second device for moving fluid through the surrogate wound andapplied to the irrigant of and towards the wound chamber is thecombination of two peristaltic pumps, pumps 1 and 2 in FIG. 33.

These act on silicone (or equivalent) elastic tubing, the internaldiameter of which was 1.0 mm.

A total volume for the circuit including the chamber and the reservoirof between 50 and 220 ml was used. The continuous flow rates used werebetween 0.1 ml min⁻¹ and 2.0 ml⁻¹ min⁻¹.

In use as a system where the wound is subjected to repeated iteration ofa cycle of fluid delivery followed by a period of aspiration to wasteunder reduced pressure, an air bleed fluid control T-valve wasadditionally positioned in the circuit upstream of the wound chamber (asshown), such that the valve may be set so that (a) the air bleed isclosed for a time and irrigant fluid flows into the wound chamber, (b)the air bleed is opened and irrigant fluid/wound exudate mixture isevacuated from the chamber and (c) air bleed and flow to the chamber areclosed off, and the fibroblasts are maintained under a negative pressurerelative to the atmosphere.

This represents an empty/fill system with cycles of empty/fill.

The following experiments were conducted using a circuit comprising awound chamber as above:

1. with a bioscaffold matrix (consisting of a Vicryl mesh (90:10polyglycollic lactic acid) coated with extracellular matrix) placed inclose proximity to the wound bed fibroblasts, (a) containing a totalvolume of nutrient media (104 ml) pumped at a continuous flow rate of0.2 ml min⁻¹, and where vacuum was set at 950 mbar and where atmosphericpressure varied up to a maximum value of 1044 mbar, over 2.5 day, and(b) operated with 11 cycles of empty/fill performed with each fill orempty phase lasting 1 hour, and where vacuum was set at 950 mbar

2. with the bioscaffold matrix replaced with a matrix consisting of anylon mesh, (a) containing a total volume of nutrient media (104 ml)pumped at a continuous flow rate of 0.2 ml min⁻¹, and where vacuum wasset at 950 mbar and where atmospheric pressure varied up to a maximumvalue of 1044 mbar, over 2.5 day, and (b) operated with 11 cycles ofempty/fill performed with each fill or empty phase lasting 1 hour, andwhere vacuum was set at 950 mbar.

Results and Conclusions

The following results were obtained:

In controls where (a) the apparatus is operated as an empty/fill systemwith 11×cycles of 1 hour empty/1 hour fill over a total of 2.5 days,and/or (b) a nylon scaffold is used, the migration, and growth of thefibroblasts is inhibited.

However, when the irrigant flow in the circuit is (a) deliveredcontinually to the surrogate wound chamber and the fluid is at the sametime continually aspirated from the surrogate wound chamber undervacuum, set at 950 mbar and where atmospheric pressure varied up to amaximum value of 1044 mbar, and (b) a bioscaffold is present, thefibroblasts migrate and proliferate to a greater extent during a 2.5 dayperiod than the control empty/fill circuits.

Mean of cell activity* Conditions after 2.5 day hours. N = 3 Continuousflow (SIA) plus 0 synthetic scaffold Continuous flow (SIA) plus 0.68bioscaffold Fill empty 6 cycles at room 0 temperature plus syntheticscaffold Fill empty 6 cycles plus 0.46 bioscaffold *Cell activity ofscaffold measured with a WST (Tetrazolium based mitochondrialdehdrogenase activity assay).

The combination of bioscaffold and continuous fluid flow at 0.2 ml min⁻¹with waste fluid removal under vacuum of no more than 10% atmosphericpressure, 950 mbar and atmospheric pressure varied up to a maximum valueof 1044 mbar, enhances the cell response necessary for wound healingmore than the empty fill regime, under vacuum.

These act on silicone (or equivalent) elastic tubing, the internaldiameter of which was 1.0 mm.

A total volume for the circuit including the chamber and the reservoirof between 50 and 220 ml was used. The continuous flow rates used werebetween 0.1 ml min⁻¹ and 2.0 ml⁻¹ min⁻¹.

In use as a system where the wound is subjected to repeated iteration ofa cycle of fluid delivery followed by a period of aspiration to wasteunder reduced pressure, an air bleed fluid control T-valve wasadditionally positioned in the circuit upstream of the wound chamber (asshown), such that the valve may be set so that, (a) the air bleed isclosed for a time and irrigant fluid flows into the wound chamber, (b)the air bleed is opened and irrigant fluid/wound exudate mixture isevacuated from the chamber and (c) air bleed and flow to the chamber areclosed off, and the fibroblasts are maintained under a negative pressurerelative to the atmosphere.

This represents an empty/fill system with cycles of empty/fill.

The following experiments were conducted using a circuit comprising awound chamber as above

1. with a bioscaffold matrix (consisting of a Vicryl mesh (90:10polyglycollic lactic acid) coated with extracellular matrix) placed inclose proximity to the wound bed fibroblasts, (a) containing a totalvolume of nutrient media (104 ml) pumped at a continuous flow rate of0.2 ml min⁻¹, and where vacuum was set at 950 mbar and where atmosphericpressure varied up to a maximum value of 1044 mbar, over 2.5 day, and(b) operated with 11 cycles of empty/fill performed with each fill orempty phase lasting 1 hour, and where vacuum was set at 950 mbar

2. with the bioscaffold matrix replaced with a matrix consisting of anylon mesh, (a) containing a total volume of nutrient media (104 ml)pumped at a continuous flow rate of 0.2 ml min⁻¹, and where vacuum wasset at 950 mbar and where atmospheric pressure varied up to a maximumvalue of 1044 mbar, over 2.5 day, and (b) operated with 11 cycles ofempty/fill performed with each fill or empty phase lasting 1 hour, andwhere vacuum was set at 950 mbar.

Example 8

Demonstration of in vitro effects of applying stress to cells in asimulated wound.

Objective

To determine the total amount of collagen deposited by human dermalfibroblasts on silica Flexercell plates following macrostress treatmentover a period of time.

Methods

Cells

Human dermal fibroblasts (HS8/BS04) were used. Experiments wereperformed whereby fibroblasts (5×10⁵ per well) were seeded in siliconemembrane 6 well plates (Flexercell), supplied by Flexcell Intl.Hillsborough, N.C. and subjected to a range of ‘macrostress’(macrostress as used in this example refers to stress applied to thecells by way of mechanical stretching) treatments for 48 hours, wherebythe cells were subjected to a strewn of 15% (i.e. 15% elongation of thecell substrate) at a frequency of 0.1 Hz on a cycle having a sine waveprofile. The Flexercell, Tension Plus™ system is a computer-driveninstrument that simulates biological strain conditions using vacuumpressure to deform cells cultured on flexible, matrix-bonded growthsurfaces of BioFlex® series culture plates. Following experimentation,media was removed, the cells were washed in PBS and stored at −70° C.until analysed for collagen levels.

The cells were exposed to sequential (SEQ) or simultaneous (SIA)irrigation/aspiration. For SIA, a flow rate of 0.1 ml per minute wasused. For sequential, 10 empty/fill cycles were performed over the 48hour period, each empty/fill taking 1 hour to complete. The media usedwas DMEM/10% FCS.

Collagen Quantification

The collagen content present on the 6 well plates was determined using ahydroxyl proline quantification assay which 2 ml papain buffer was usedto digest any collagen due to the larger surface area.

RT-PCR

Relative quantification of plasminogen inhibitor activiator 2 (PIA-2)amd collagen 1a gene expression was determined using the Taqman RT-PCRmachine.

RNA Extraction

Cells were scraped from the well in RLN buffer and the RNA from 3 samplewells were pooled using one RNeasy mini column. Control RNA wasextracted from fibroblasts grown to confluence in a T175 flask.

RNA extraction from fibroblasts was performed using reagents andprotocols described in RNeasy Mini Handbook (Qiagen) and RLN buffer (50mM Tris-HCl, Sigma, lot 033K8418; 140 mM NaCl, Sigma, lot 013K8930; 1.5mM MgCl₂, Sigma, lot 082K8938; 0.5% (v/v) Igepal (Sigma, lot 102K0025);10 μl/ml β-mercaptoethanol, Sigma, lot 102K0025, made up to volume inMolecular Biology grade water (Sigma, lot, 23K2444).

Following elution from the spin column in 50 μl water, the RNA wasquantified using a spectrophotometer.

cDNA Preparation

cDNA was prepared from RNA using Omniscript reverse transcription kit(Qiagen) with Random Hexamer primers (Applied Biosystems, lot G07487).The reaction was completed by heating for 1 hour at 37° C. and stored at−20° C. until required.

RT-PCR Primers

Three gene products were selected as they had previously been shown tobe up-regulated during Flexercell Macrostress treatment (Kessler, et al,JBC, 276, 39, 36575-36585, 2001). Primers were synthesised by MWGBiotech.

Collagen 1a: F- 5′ ACA TGC CGA GAC TTG AGA CTC A R- 5′GCA TCC ATA GTA CAT CCT TGG TTA GG(from Wong et al, Tissue Engineering, 8, 6, 979-2002) PAI-2: F- 5′AAT GCA TCC ACA GGG GAT TA R- 5′ CGC AGA CTT CTC ACC AAA CA(Designed using Primer 3 software, sequence from accession no. H81869)18S rRNA F- 5′ CGG CTA CCA CAT CCA AGG AA R- 5′ GCT GGA ATT ACC GCG GCT

(18S rRNA housekeeping gene primers previously designed and synthesisedby Sigma).

SYBR Green

SYBR green reagent (Applied Biosystems, lot 0505023) master mix wasprepared as per manufacturers protocol. Briefly, 50% v/v SYBR green,0.05% primer 1, 0.05% primer 2, made up to 100% in RNase free water. 5μl cDNA template and 45 μl SYBR green added per well.

PCR

The RT-PCR was performed using 7700 Taqman RT-PCR system (SOP/BC/227).The run conditions were: (1) 50° C. for 2 minutes, (2) 95° C. for 10minutes, (3) 95° C. for 15 seconds, (4) 60° C. for 1 minute.

Conditions 3 and 4 repeated for a total of 40 cycles.

To ensure a single PCR product had been amplified, a melt analysis onthe product was performed using the following conditions: (1) 95° C. for15 seconds, (2) 60° C. for 20 seconds, (3) 95° C. for 15 seconds

A ramp time of 19.59 minutes between stage 2 and 3 was used to determinethe degradation temperature.

Discussion

Collagen Quantification

The amount of collagen present in each well of a six well Flexercellplate was determined using the hydroxyproline quantification assay.Fibroblast cells, seeded at either 5×10³ or 5×10⁵ per well were grown onlaminin coated plates for 72 hours. The absorbance values determinedfollowing analysis were very low, showing that the amount of collagenpresent was also very low. Unfortunately, an error was made whenpreparing the hydroxyproline standard curve whereby the stock solutionwas not diluted 10 fold so it was not possible to give an amount ofhydroxyproline present. This error would only have affected thestandards. The low values showed that this assay was not suitable formeasuring such low collagen contents.

A second hydroxyproline determination assay was performed using gaschromatography (GS-MS). This analysis also revealed very low collagencontent present in the 6 well plates.

RT-PCR

As the cells only had 72 hours to proliferate and synthesis newcollagen, a short length of time, it was decided to look for changes inthe level of gene expression, which, generally relates to changes in theamount of protein synthesised as the cells proliferate.

The genes of interest chosen to investigate were collagen 1a andplasminogen activator inhibitor 2 (PIA-2) genes as these had previouslybeen shown to be induced in stressed collagen lattices (Kessler et al,JBC, 276, 39, pp 36575-36585, 2001). The level of gene expression of thegenes of interest is expressed as a ratio against 18S rRNA, ahouse-keeping gene, shown previously (Kessler et al, 2001) to remain ata steady level of expression.

For the RT-PCR experiments, fibroblasts were grown and subjected to 15%strain, 0.1 Hz frequency for 48 hours, with control samples not beingsubjected to these conditions. Also, they were subjected to eithercontinuous irrigate aspiration of media (SIA), or a series of 1 hourempty/fill cycles (SEQ). All systems were kept under vacuum of ˜25 mbarbelow atmospheric.

The level of PAI-2 gene expression was determined in fibroblastssubjected to the four sets of conditions described above. The resultsare shown in the table below.

SIA only 1.6 SEQ only 5.3 SIA plus macrostress 5.4 SEQ plus macrostress5.3

The results show that there is an increase in the level of PAI-2 geneexpression when fibroblasts in the SIA system are subjected tomacrostress (at 15% strain, 0.1 Hz frequency; n=1). However, the levelof expression is also elevated in both SEQ and SEQ plus macrostressfibroblasts. Unfortunately, due to technical difficulties during theinitial macrostress Flexercell experiments, only one set of experimentalplates were available for analysis.

Results and Conclusions

RT-PCR analysis of PAI-2 gene expression showed an increase in the levelof expression in SIA plus macrostress compared to SIA only. Thisdemonstrates the effect of macrostress on the activity of the cells inthe in vitro wound simulation, and supports the role of macrostress inwound healing.

There was no difference in the level of expression in SEQ and SEQ plusmacrostress fibroblasts.

Due to technical difficulties, these results are from an n=1, thereforecare needs to be taken when interpreting the results. However, theresults indicate that application of macrostress to cells during SIAirrigation leads to increase levels of cell activity, and possibly ofcollagen production. This reflects on increase in healing activity wherestress is applied.

The results of the SEQ analysis are puzzling, and may be the results ofan unidentified error in the protocol. Future experiments will berequired to confirm this. An alternative hypothesis is that additionalstresses induced by the fill/empty cycle may have inadvertently resultedin stress being applied to the control population.

Example 9

In vitro example demonstrating the efficacy of the Flow Stress instimulating cell activity in a wound model.

An apparatus of the present invention was constructed essentially as inFIG. 33.

The circuit has the means for fluid cleansing of a wound using anapparatus where an irrigant or fluid of some nature is deliveredcontinually to the wound bed and the resultant wound exudate/fluidmixture is at the same time continually aspirated from the wound and ispumped to waste (i.e. simultaneous aspiration/irrigation—SIA). The cellchamber (400) representing the wound bed is held under vacuum tosimulate negative pressure (pressure range <10% atmospheric). (For theexperiments the aspirant was not pumped to waste but was re-circulated).The circuit was also used to provide a system where the wound issubjected to repeated iteration of a cycle of fluid delivery followed bya period of aspiration under reduced pressure (i.e. sequentialirrigation/aspiration—SEQ).

The apparatus comprised a surrogate wound chamber (400) (Minucellsperfusion chamber) in which normal diploid human fibroblasts werecultured on 13 mm diameter (Thermanox polymer) cover slips retained in atwo part support (Minnucell Minusheets). Tissues present in the healingwound that must survive and proliferate were represented by the cellswithin the chamber. Nutrient medium (DMEM with 5% FCS with 1% BufferAll) to simulate an irrigant fluid/wound exudate mixture was pumped froma reservoir into the base of chamber where it bathed the fibroblasts andwas removed from the top of the chamber and returned to a secondreservoir. The wound chamber was maintained at less than atmosphericpressure by means of a Vacuum pump (18A) in line with the circuit. Anair bleed fluid control valve was additionally positioned in the circuitso that on opening the air bleed for a time and closing the fluid flow,the simulated irrigant fluid/wound exudate mixture was evacuated fromthe chamber and the fibroblasts were maintained in a moist environmentunder a negative pressure relative to the atmosphere.

The pumps for the circuit were peristaltic pumps acting on silicone (orequivalent) elastic tubing. The circuit was exposed to a vacuum of nomore than 10% atmospheric pressure, (with a range of 950 mbar to 1044mbar). The internal diameter of the tubing was 1.0 mm. A total volumefor the circuit including the chamber and the reservoir was between 50and 220 ml. The flow rates used were at 0.1 ml min⁻¹

Circuit comprised of an upstream of the wound chamber, a heat exchangersuch that the temperature of the nutrient media bathing the cellsreaches between 35° C. and 37° C.

Experiments were conducted that simulated conditions not uncommon forhealing wounds whereby the nutrient media delivered to the wound sitewas supplemented by microstress (the term microstress is used in thisexample to relate to flow stress) provided by increasing the rate ofmedia flow over the cells to 1.4 ml min⁻¹ for 6 hours.

An experiment was conducted that simulated conditions that are notuncommon for healing wounds whereby a fluid was delivered to the woundbed and the application of a vacuum is used to remove the mixture offluid and exudate to a waste reservoir whereby an air bleed fluidcontrol valve was additionally positioned in the circuit so that onopening the air bleed occurred for a time and closed the fluid flow, thesimulated irrigant fluid/wound exudate mixture was evacuated from thechamber and the fibroblasts were maintained under a negative pressurerelative to the atmosphere. This represents an empty/fill system, 10cycles of empty/fill were performed with each fill or empty phaselasting 1 hour.

Circuit apparatus were constructed essentially as in FIG. 2 above andconsisted of: (a) a control system which contained: (i) empty/fillsystem with 10×cycles of 1 hour empty/1 hour fill over a total of 48hours and (ii) the chambers representing the wound bed were exposed tomicrostress; or (iii) The chambers representing the wound bed were NOTexposed to microstress; (b) The test apparatus: (i) a continuous flowsystem over a total of 48 hours and (ii) the chambers representing thewound bed were exposed to microstress; or (iii) the chambersrepresenting the wound bed were NOT stimulated by microstress treatment

Method in More Detail

Cells

Human dermal fibroblasts (HS8/BS04) grown at 37° C./5% CO₂, in T175flasks containing 35 ml DMEM/10% FCS media were washed in PBS and liftedusing 1×trypsin/EDTA (37° C. for 5 min). Trypsin inhibition was achievedby adding 10 ml DMEM/10% FCS media and the cells pelleted bycentrifugation (Hereus Megafuge 1.0R; 1000 rpm for 5 min). The media wasdiscarded and cells re-suspended in 10 ml DMEM/10% FCS. Cells werecounted using a haemocytometer and diluted in DMEM/10% FCS to obtain100,000 cells per ml.

Cells (100 μl of diluted stock) were transferred to each 13 mm Thermanoxtissue culture coated cover slip (cat. 174950, lot 591430) in a 24 wellplate and incubated for 1 hr at 37° C./5% CO₂ to allow cell adherence.After 1 h, 1 ml DMEM/10% FCS media was added per well and the cellsincubated overnight in the above conditions.

Following overnight incubation, cells were assessed visually for growthunder the microscope and those with growth were inserted into cover slipholders (Vertriebs-Gmbh, cat no. 1300) for assembly in the Minucellchamber (Vertriebs-Gmbh, Cat no. 1301).

Media

Cells were grown in DMEM media (Sigma, no. D6429) supplemented with 10%foetal calf serum; 1-glutamine, non-essential amino acids andpenicillin/streptomycin (various lot numbers). Media used in theexperimental systems was buffered with Buffer-All media (Sigma, lot75K2325) to ensure stable pH of the media.

Minucell Flow Systems

Systems (4) were made up as follows: a) SIA (simultaneous irrigateaspirate) only, (b) SEQ (sequential irrigate aspirate) only, (c) SIAplus microstress, (d) SEQ plus microstress

Media (50 ml) was transferred to each reservoir bottle. The Minucellchambers were filled with 4 ml media and 6 coverslips inserted. Thesystems were set-up as shown in FIG. 30 (the pumps were set to run at0.1 ml/min); hot plates set to 45° C.; Discofix 3-way valves (Arnoldslot 04A2092042 c/z); vacuum pump (Ilmvac VCZ 324, asset no 6481, set to950 mbar).

Media was circulated at 0.1 ml/min continuously. In empty/fill systems,the Minucell chambers were emptied by stopping the media flow andswitching the 3-way valve to allow air through an attached 0.22 μmfilter. When fully emptied, the 3-way valve was closed between the valveand the pump and kept under vacuum. Elevation of the 3-way valve ensuredmedia did not pass through the 0.22 μm filter by gravity flow. After 1h, the 3-way valve was switched back to the starting position to allowthe Minucell chamber to fill and flow rate returned to 0.1 ml/min.Continuous irrigate/aspirate systems were run continuously under vacuumat 0.1 ml/min for 48 h.

The vacuum pump was set to 950 mbar. The atmospheric pressure varieddaily, up to a maximum value of 1044 mbar; therefore the difference inpressure between the systems and the atmosphere was always under 10%.The fill/empty systems were treated as per the table below.

Microstress (i.e. Flow Stress)

Microstress stimulation was provided by increasing the flow rate of themedia in the system to 1.4 ml/min for the first 6 hours of theexperiment. The flow rate was then returned to 0.1 ml/min

Fill/empty regime for Minucell chambers.

Day 1—4 × empty/fill cycles Day 2—4 × empty fill cycles Day 3—2 ×empty/fill cycles and WST assay

WST Assay

A WST assay to measure the cells mitochondrial activity was performed on6 coverslips from each system. WST reagent (Roche, lot 102452000) wasdiluted to 10% v/v in DMEM/5% FCS/buffer all media. The coverslips wereremoved from the Minucell chamber and washed in 1 ml PBS. PBS wasremoved and 200 μl WST/DMEM media added. The coverslips were thenincubated at 37° C. for 45 min before transferring 150 μl to a 96 wellplate. The absorbance at 450 nm with reference at 655 nm was determinedusing Ascent Multiskan Microtitre plate reader.

Results and Conclusions

The following results were obtained for a circuit comprising a woundchamber as above containing a total volume of nutrient media (104 ml)pumped at a flow rate of 0.1 ml min⁻¹ and where vacuum was set at 950mbar and where atmospheric pressure varied up to a maximum value of 1044mbar. The wound chamber and media were held at 37° C. for 48 hours andexposed to microstress. In one set of wound chambers continuous flow wasmaintained. In a second set of chambers 10 cycles of empty/fill wereperformed with each fill or empty phase lasting 1 hour.

In samples where either (a) empty/fill system with 10×cycles of 1 hourempty/1 hour fill over a total of 48 hours, or (b) the exposure tomicrostress is omitted, the survival and growth of the fibroblasts isgenerally relatively poor.

However, when the nutrient medium flow in the first circuit is (a) isdelivered continually to the Minucell chamber and the resultant nutrientmedium is at the same time continually aspirated from the Minucellchamber under vacuum, and (b) is exposed to microstress, the fibroblastssurvive and proliferate to a far greater extent during a 48 hour periodthan the control empty/fill circuits.

The results are shown in the following table.

Mean of cell activity* Conditions after 48 hours. N = 2 Continuous flow(SIA) flow 0.54 Continuous flow (SIA) 0.61 plus)microstress Fill/empty10 cycles 0.28 Fill empty 10 cycles plus 0.51 microstress *Cell activitymeasured with a WST (Tetrazolium based mitochondrial dehdrogenaseactivity assay).

The combination of microstress and continuous fluid flow at 0.1 ml min⁻¹with waste fluid removal under vacuum of no more than 10% atmostphericpressure, (950 mbar and atmospheric pressure varied up to a maximumvalue of 1044 mbar) resulted in an improvement in the healing responseof the cells. In the fill empty cycle system the improvement was evenmore pronounced, resulting in an almost doubling of cell activity.

These results suggest that application of microstress (i.e. flow stress)to a wound in both simultaneous and sequential irrigate/aspirate systemsmay be of significant benefit to wound healing.

Example 10

Using simultaneous irrigate/aspirate (SIA) and sequentialirrigate/aspirate (SEQ), the effect of cells as a source of ‘actives’ onfibroblast proliferation was determined.

Method

Cells

Human dermal fibroblasts (HS8/BS04) grown at 37° C./5% CO₂, in T175flasks containing 35 ml DMEM/10% FCS media were washed in PBS and liftedusing 1×trypsin/EDTA (37° C. for 5 min). Trypsin inhibition was achievedby adding 10 ml DMEM/10% FCS media and the cells pelleted bycentrifugation (Hereus Megafuge 1.0R; 1000 rpm for 5 min). The media wasdiscarded and cells re-suspended in 10 ml DMEM/10% FCS. Cells werecounted using haemocytometer (SOP/CB/007) and diluted in DMEM/10% FCS toobtain 100,000 cells per ml.

Cells (100 μl of diluted stock) were transferred to 13 mm Thermanoxtissue culture coated cover slips (Fisher, cat. no. 174950, lot no.591430) in a 24 well plate and incubated at 37° C. in 5% CO₂ to allowfor cell adherence. After 1 h, 1 ml DMEM/10% FCS media was added perwell and the cells incubated for approximately 5 hours in the aboveconditions. Cells were serum starved overnight by removing the DMEM/10%FCS and washing the coverslips with 2×1 ml PBS prior to the addition of1 ml DMEM/0% FCS.

Following overnight incubation, cells were assessed visually for celladherence under the microscope and those with good adherence wereinserted into cover slip holders for assembly in the Minucell chamber.

Media

Cells were grown in DMEM media (Sigma, cat. no. D6429) supplemented with5% foetal calf serum; 1-glutamine, non-essential amino acids andpenicillin/streptomycin. Media used in the experimental systems wasbuffered with 1% (v/v) Buffer-All media (Sigma, cat. no. B8405, lot. no.51k2311) to ensure stable pH of the media.

Minucell Flow Systems

Media (50 ml) was transferred to each bottle prior to the autoclavedsystems being assembled. The Minucell chambers were filled with 4 mlmedia prior to coverslips being inserted. The systems were set-up asshown in FIG. 29, set to run at 0.2 ml/min; hot plates, set to 45° C.;Discofix 3-way valves; vacuum pump, (IImvac VCZ 310), set to 950 mbar).

SEQ Systems

Media was pumped through the systems at 0.2 ml/min continuously when thechambers were full. The Minucell chambers were emptied by disconnectingthe tubing from the pump and switching the 3-way valve to allow airthrough an attached 0.22 μm filter. When fully emptied, the 3-way valvewas switched to close the system between the valve and the pump and soallowing the formation of a vacuum in the system. Elevation of the 3-wayvalve ensured media did not pass through the 0.22 μm filter by gravityflow. After 1 h, the 3-way valve was switched back to the startingposition to allow the Minucell chamber to fill and the tube reconnectedto the pump. The SEQ systems were treated as per the following table.

Fill/empty regime for SEQ systems.

Time (h) 0 1 2 3 4 5 6 7 8 20 21 22 23 24 Empty/fill F E F E F E F E F EF E W A F = full chamber/flowing; E = empty chamber/under vacuum; W =remove coverslips for WST assay; A = read WST assay result.

SIA Systems

Continuous irrigate aspirate systems were run for 24 h with mediairrigating the cells and being aspirated under vacuum set to 950 mbar.The atmospheric pressure varied daily, up to a maximum value of 1048mbar, therefore the difference in pressure between the systems and theatmosphere was always under 10%.

Cells as Actives Component

The ‘cells as actives’ component of the flow cell system was provided byDermagraft (a fibroblast seeded Vicryl mesh). Dermagraft stored at −70°C. was defrosted by placing in a 37° C. water-bath for 1 min and washed×3 with 50 ml 0.9% v/v NaCl. The Dermagraft was cut into 24×1.1 cm²squares using a sterile clicker-press and placed into DMEM/5% FCS. Forthe flow-cell experiments, a number of Dermagraft squares were placed inMedia 1 bottle (FIG. 1) immediately prior to the start of theexperiment. The presence of live cells in the Dermagraft squares wasdetermined by WST assay when the experiment was terminated.

WST Assay

A WST assay to measure cell mitochondrial activity was performed on thecoverslips. WST reagent (Roche, cat. no. 1 644 807, lot no. 11264000)was diluted to 10% v/v in DMEM/10% FCS. The coverslips (n=6) wereremoved from each Minucell chamber and washed in 1 ml PBS. PBS wasremoved and 200 μl WST/DMEM media added. The coverslips were thenincubated at 37° C. for 45 min before transferring 150 μl to a 96 wellplate. The absorbance at 450 nm with reference at 655 nm was determinedusing Ascent Multiskan Microtitre plate reader.

Results and Conclusions

The mitochondrial activity of cells grown in SIA and SEQ systems, withor without ‘cells as actives’ component was determined using the WSTassay. The optimal number of Dermagraft squares required was firstassessed in a SIA flow cell system. Addition of Dermagraft squares tothe media had a beneficial effect, increasing the proliferation rate ofseeded fibroblasts (FIG. 34). There was a slight benefit to increasingthe number of Dermagraft squares from 3 to 6, although increasing theamount of Dermagraft to 11 squares did not further increase the rate ofproliferation. Therefore, for the flow cell experiments, 6 Dermagraftsquares were placed in the relevant media bottles. The experiments toshow the optimal number of Dermagraft squares also showed that theaddition of cells as a source of actives, to the SIA systems, resultedin an increased rate of proliferation (FIG. 34).

Treatment of fibroblasts by the addition of ‘cells acting as a source ofactives’ to the media, increased the rate of proliferation in SIA andthe SEQ systems after 24 hours (FIGS. 34 & 35).

This beneficial effect was observed in both SAI and the SEQ flowsystems.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the device or process illustrated may be madewithout departing from the spirit of the disclosure. Additionally, thevarious features and processes described above may be used independentlyof one another, or may be combined in various ways. All possiblecombinations and subcombinations are intended to fall within the scopeof this disclosure. Many of the embodiments described above includesimilar components, and as such, these similar components can beinterchanged in different embodiments.

Although the invention has been disclosed in the context of certainembodiments and examples, it will be understood by those skilled in theart that the invention extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses and obviousmodifications and equivalents thereof. Accordingly, the invention is notintended to be limited by the specific disclosures of preferredembodiments herein.

What is claimed is:
 1. An apparatus comprising: a wound dressing; afluid container having an inlet and an outlet; a tube configured toconnect the wound dressing to the fluid container, thereby forming afluid flow path; a filter positioned downstream of the inlet; aperistaltic pump configured to pump fluid through the tube, theperistaltic pump isolated from the fluid flow path; and a pressurecontrol valve on the fluid flow path, positioned between the wounddressing and the peristaltic pump, upstream from the filter.
 2. Theapparatus of claim 1, wherein the pressure control valve comprises arotary valve.
 3. The apparatus of claim 1, wherein the filter comprisesa microscopic filter.
 4. The apparatus of claim 1, wherein the wounddressing comprises a backing layer, the backing layer configured to forma fluid-tight seal over a wound.
 5. The apparatus of claim 1, furthercomprising a port configured to connect to atmosphere.
 6. The apparatusof claim 5, further comprising a bleed valve connected to the port. 7.The apparatus of claim 5, wherein the port is connected to an offtaketube.
 8. The apparatus of claim 5, wherein the port is connected to apressure monitor.
 9. The apparatus of claim 6, wherein the bleed valvecomprises a motorized valve.
 10. The apparatus of claim 9, wherein themotorized valve comprises a rotary valve.
 11. The apparatus of claim 1,wherein the fluid container is flexible.
 12. The apparatus of claim 11,wherein the fluid container comprises a collection bag.
 13. Theapparatus of claim 1, wherein the peristaltic pump is positionedupstream from the fluid container.
 14. The apparatus of claim 1, whereinthe wound dressing comprising a porous layer.
 15. The apparatus of claim14, wherein the porous dressing comprises foam.